Allys
In this situation I think you need to sit down with a financial advisor. There will be alot of questions and issues to think about.
Has the house been sold and the £20k banked? If so you may wish to get some advice about whether paying off any of your debts will improve your credit rating to make any difference with a new Mortgage application.
Who is the main earner that would be first name applicant on the Mortgage? If this is your girlfriend could she apply for the Mortgage in her name only? If this is possible, perhaps once you have cleared your debts and improved your credit score, you can be added to the Mortgage at a later date. From what I understand, however, if companies are lending only 3.5X salary, she would need to be on atleast £40k, to afford a £150k property in her sole name.
If you are to be party to the Mortgage I would think that your debts and credit score will count against you. This is because these debts may cause you difficulty in being able to make repayments and the companies you owe money to, could take proceedings against you. Therefore I doubt you can get a mortgage in your current circumstance, as from what I have read others in a better position are being turned down, as lenders are being very picky.
If I were in your position I would use the money to pay off the debts, provided there was not any penalty for early repayment. I would then rent for awhile, rebuild my credit rating by being careful for a few years and then look at getting back on the housing ladder. If you invest any money you have left over, you may build up a reasonable deposit again.This will be a much better way, than paying interest/fees on debts and hassle from bank/loan companies. If you are thinking house prices have bottomed out and now is the time to buy again, I think it is too early to tell. Getting credit is difficult and this will continue for awhile. If a were a betting man, I would put money on, that house prices will not start to increase by any significant amount until after the next general election June 2010.
huckster