As has been suggested, you need to find out more details about your loan, Paddy.
For a start, if you have been paying £25 per month more than the interest why has the amount you owe increased so dramatically? If you are paying just £25 a month off the principle (the amount borrowed) it will take something around nineteen years to pay off the loan but nonetheless the amount you owe should decrease steadily not increase by over 50% in six years. Also, £115 per month interest on a loan of this size equates to an interest rate of about 24% which is very hefty for a secured loan. (Credit card companies only charge about 20% on outstanding balances).
To give you some idea of a comparison with a high street bank, if you borrowed £5,700 from Lloyds you would pay £126 per month and the loan would be cleared in five years. You need to get all the papers for this loan together and show them to an advisor (the Citizens Advice Bureau might help). It seems to me you are being turned over.