Liberal Democrats in Oxford have lost their third high-profile councillor in nine months.

Tia MacGregor, a GP and mother-of-two, who represents Quarry & Risinghurst, said the party "was no longer working for her" and would now sit as an Independent councillor.

Dr MacGregor, who will tell her Liberal Democrat colleagues today she is resigning from the party, follows on the heels of former Lib Dem city councillor Paul Sargent who now sits as an independent.

He left the group in May last year after losing out to Patrick Murray in a vote for a position on the decision-making executive.

A month later, Sajjad Malik crossed the floor to join Labour from the Lib Dems, blaming infighting and a lack of commitment towards building homes on the edge of the city as his main reasons.

Today, the Lib Dem's control of the city council is precarious - although the party could rely on her vote at last night's budget meeting.

John Goddard's group now runs the authority with just 16 councillors - two fewer than Labour's 18.

The Greens have eight, while the Independent Working Class Association has four.

Dr MacGregor said: "I have for some time now felt the direction the Lib Dem party was going in was different to mine.

"After long thought and careful consideration I have become convinced that the best way to serve my ward is to resign the party whip and for now to sit as an independent on Oxford City Council.

"I would like to reassure residents of Quarry and Risinghurst I will continue to represent their interests effectively."

Dr MacGregor, who lives in Burrows Close, Headington, said there was no single reason why she was leaving the Lib Dems.

She added: "Being in party doesn't seem to be working for me. I suppose that without any party strings, I will be more able to represent people in Oxford."

Because the city council is hung, the Lib Dem ruling group is increasingly reliant on support from other groups.

Since the Lib Dems took control of the Town Hall in May last year, the group has been beset by allegations of infighting and personal differences.

When Mr Sargent left the Lib Dems he diplomatically said: "I still share many of the principles and policies of the Liberal Democrats, but sometimes you have to go in a different direction."

Dr MacGregor, who was elected in 2004 and due for re-election in 2008, joins a lengthy list of recent city council defectors.

Sarah Margetts left Labour to become an independent in January, 2002, Mick McAndrews switched from Lib Dem to Labour in May, 2000 and Bob Hoyle left Labour to join the Lib Dems in April the same year.