The Child Support Agency is chasing more than 4,300 Oxfordshire parents for failing to pay £11m towards the upkeep of their children - an average of £2,700 per family.o New figures published by the Conservative Party, see table below, show how much is owed in each Parliamentary constituency.

The figures come as no surprise to one woman from Banbury, who has finally given up on her CSA claim after 11 years.

Mother-of-two Jane Smith, 48, estimates she is owed £45,000 by her ex-husband.

She said: "I'm sure mine is just one of thousands of typical cases.

"My children are now 12 and 14 and their dad left when they were one and three. Straight away, I contacted the CSA and told them about this change in my circumstances.

"I filled in the forms and was told it would all be pretty straightforward.

"But there has only been one period of about six months during the last 11 years when I have received any money from my ex, and that was when it was taken straight from his wage packet.

"Since then, he has moved houses, changed jobs and even resigned from a job, because each time his circumstances change, he has to be reassessed and that takes weeks."

Ms Smith feels the CSA has also failed her.

She said: "I have spent so many hours on the phone, waiting, being redirected and not being phoned back when they said they would. Not once have I spoken to my case worker.

"My children have gone without so much."

Ken Webb, 40, who lives near Banbury, said not all absent dads should be penalised by the CSA.

He said: "Not all dads refuse to pay. I have always been prepared to pay for the child I had from a previous relationship and told the CSA that.

"But when I changed my jobs and contacted them, they didn't send me the forms they should have and, as a result, I was later told I had to pay huge arrears.

"Eleven years on, I am still struggling to pay while supporting my partner and our two children."

In 2006, the Government invested £120m in the CSA, adding 1,000 new staff.

It is hoped a new Child Maintenance and Enforcement Commission will help improve collection from 2010.