I am a mortgage broker based in Northern Ireland and I can tell you that you have many choices and most of what you are saying is unlikely to happen anymore if your credit is in reasonable shape and you have had no further problems since the default 5 years ago.
As it happens I am dealing with a first time buyer at present and they have a 5 year old default and I have got them accepted at 85% borrowig so a remortgage of 41% or less is not going to be much of a problem if you have been good with your credit and mortgage over the last couple of years
Ascenden will not give you another product purely and simply on the basis that they no longer lend money and have gone out of business as a mortgage lender.
With a 5 year old deault it may raise an eyebrow with some lenders but because the risk they are taking on is very low I doubt that many lenders will say no (Ulster Bank and Northern Bank will say no though). If you approach any mortgage broker they will be able to show you the whole market as it stands and move you towards a lender that will be sympathetic towards your past histoy and should be able to find you a product around 3%-3.5%. The cost of the mortgage will of course depend on the term of repayment but an interest only mortgage at these rates would be around £110 per month
The fact that you are looking to move towards repayment instead of interest only will give the lenders confidence in your application too.
So far as fees payable upfront. There are more and more lenders that are asking for a "booking fee" which is often £99 - £199 upfront fee but as your mortgage is so low I would be looking for a totally fee free mortgage so there would be no arrangement fee, no booking fee, no valuation fee, no legal fees to set up the new mortgage. You will pay a slighty higher interest rate for accessing such products but as your mortgage balance is quite low it will have a far lesser affect on it than taking a lower rate and a fee of say £999.
Speak to a mortgage broker (not a banks mortgage monkey) and he can give you a list of such products. I would even go so far as to say that the broker should do this without a broker fee too or at least at a low cost broker fee. If you offer to let the broker review your mortgage related insurances he will most likely let you pay no fee to him as he could earn quite a good fee on commission from insurances