Talk to a mortgage advisor.
Remember that 3 years fixed at 5.52% with Abbey could well be worse than 3 years fixed at 6% with someone else if Abbey's charges are high. Remember also that, in 3 years, you will have to go through the whole process again with another lot of fees. Personally I favour mortgages that last for longer.
The mortgages that will be availble for you and your property will be different to the mortages that will be available to someone else so, in my view, you should speak to a mortgage advisor to see if there is anything available for you that you like better than the Abbey deal.