THERE is no doubt about it, Exeter College Chapel, one of Oxford's great glories, is scrubbing up well. In recent weeks, workmen have taken to using toothbrushes to remove black soot off the vast walls and ceilings, in what must be one of the most painstaking restorations ever to have been undertaken at an Oxford college.

Since early January, this masterpiece of the Gothic Revival has been filled with scaffolding and ladders.

And bit by bit, workmen previously engaged in the massive restoration of St Paul's Cathedral have been releasing gems, which have been encased in the thickest of dirt for decades.

Making visible the fine church bosses and engravings has been something of a bonus, for, in truth, the state of the decaying chapel left Exeter with little choice but to get on with extensive repairs.

Constant reminders of the problem rained down on college members in the form of small pieces of stone and crumbling concrete, which, over many months, have been dropping off the chapel into the college quad.

At the same time, the challenge for visitors has been, not so much to admire the decaying gargoyles, but to work out what they actually are.

What makes the restoration project extraordinary, however, is the college's decision to have 150 years of decay put right in one go - with the work stretching over 16 weeks.

The bill for the outside repair work alone will exceed £1.5m. The cost of all the indoor work has been paid for by a wealthy businessman with a close association with the college.

The chapel has many claims to fame, whether we are talking tapestries by William Morris and Edward Burne-Jones, founders of the Pre-Raphaelite Movement, or as the place where Inspector Morse collapsed in the famous final episode.

The chapel also figures in Philip Pullman's His Dark Materials trilogy.

Although renamed as Jordan College, Pullman, an ex-Exeter man himself, leaves little doubt that he is taking his readers into the Gothic splendour of his old college.

While many mistake it as medieval, Exeter Chapel was designed by that most famous of Victorian architects, George Gilbert Scott, whose work includes the Martyrs' Memorial, Oxford, and the Albert Memorial in London.

It was consecrated in 1859 by Samuel Wilberforce, one of the most celebrated Bishops of Oxford.

Towering over the front quad, many immediately noted its resemblance to the Sainte Chapelle in Paris, while its spire was, and remains, an unmistakable part of the Oxford skyline.

Contemporaries commented on "the dazzling whiteness of the interior." But that was when the Bath stone was new and clean.

It looked very different by the time the present bursar, Eric Bennett, arrived at the college three years ago.

If the chapel itself is a bold statement of the splendours of Victorian architecture, the bursar has no doubt that the Victorians, those ever self-confident pursuers of progress, are to blame for transforming the bright church interior into something altogether darker.

"The church was lit with two huge gas chandeliers," the bursar told me as we picked our way down the chapel nave.

"They left everything covered in soot."

As workmen got to work with water, and in some cases washing-up brushes and toothbrushes, the lost secrets of the famous church became apparent.

"There are, in fact, four different types of marble," said Mr Bennett. "It really is very colourful."

Then there are the huge bosses, high up and so blackened that it had become impossible to even identify what the stone carvings actually were.

Mr Bennett was one of the first to see some of the 29 bosses close up for the first time in 150 years, when he climbed up to inspect the newly-cleaned ceiling. The high standards of Victorian craftsmanship could once again be fully appreciated.

It turned out that they were highly-decorative floral bosses.

"The carvings were highly decorative and detailed." said the bursar. "A huge amount of artistic licence had, in fact, been taken. When you get close up you can see that they are strawberries but with blackcurrant leaves."

Many of the stained-glass windows have had to be carefully removed, piece by piece, including the chapel's huge Rose Window, with the lead around many of them having badly deteriorated.

But, then, it seems the Victorians often had to skimp on lead, even in their showpiece buildings, apparently because of the huge hunger for the metal from the Empire's military men during the Crimean War.

Outside it is the very soft sandstone, used to create the chapel, taken from a quarry near Witney, that stored up problems in this century.

Ongoing repairs have had unhappy results as Mr Bennett explained.

"When repairs were carried out, they used a lot of concrete, which was harder than the stone. So, it effectively served as wedge, splitting the stone. We've had lots of bits falling off into the quad."

Now great effort has been taken to ensure that the stone used to repair the walls will come from the very same Oxfordshire quarry.

A lectern and carved alms box are just about all that survives from the college's Jacobite chapel, which by 1843 was considered insecure and dangerous.

The Victorian church undoubtedly dominates the college, although for some, the scale of Gilbert Scott's church makes it too overbearing, easily overpowering the domestic buildings of the college's front quadrangle.

But it turns out the architect can hardly be blamed for that, as the chapel was not meant to be built on the site where it stands today. In true Oxford style, that came about by accident.

An ongoing college debate about plans for a library, the Rector's House and the Broad Street Gate, before work on the chapel was under way, resulted in Scott's magnificent chapel being erected in the wrong place.

The late switch has meant the chapel is entered through a side door, not through a grand axially from the west, as the architect had originally proposed.

But that has not stopped it becoming a firm favourite with Oxford visitors and as a wedding venue for members of the college.

The work is now ahead of schedule and the college will be holding a service celebrating the completion of the restoration at the end of the month, by which time only one stained glass window is likely to be missing.

There is no record of the men who built the church. But Exeter is now thinking of erecting two boards in the chapel, one naming benefactors and the other to recognise those who actually carried out the work.

Mr Bennett said: "Normally churches carry on the work as they raise the money. But we did not want it to be a long, slow death. What we wanted, as far as possible, was to minimise the disruption during term time."

Remarkably, for all the work, services have continued to take place in the chapel throughout the restoration. For all the clutter and scaffolding, one American couple with links to the college, even managed to get married in the chapel a few weeks ago.

Chaplain Dr Helen Orchard said: "My attitude has been that the show must go on. Originally, we were told that we would be unable to use the back pews. But once we saw all the scaffolding going up, it was apparent that we would be losing much more space than that.

"The work means that everything is in the wrong place. We even had to move the altar at one point, otherwise it would have been under scaffolding. The low point for me was when they strung up safety lights right up above the altar.

"But it is just short-term pain. Once the work is finished by Easter, it is going to look fantastic. It is one of the most beautiful chapels in Oxford. People have always come to see the stained-glass windows and the tapestries by Morris and Burne-Jones. Now they can enjoy the clean stone work. It has changed the whole feel of the place."

The opportunity is also being taken to add a loop listening system into the chapel, which will greatly benefit members of the congregation with hearing aids.

It has also offered an intriguing chance to fill some of the eight empty niches with figures on the Broad Street side of the chapel. Members of college are now debating what, or who, should go in the niches. Some favour traditional figures to match saints on the other side, while others would like to see famous alumni.

The case for Inspector Morse, who spent so much time singing at the chapel, has still to be made.