Subrogation means taking over a mortgage, keeping the same conditions. if you are buying from a developer then it means taking the mortgage that they already have in place and the interest rate and term will be be as what is on offer. The conditions cannot be changed. By doing this fees and taxes are lower, e.g. there is no valuation fee, no stamp duty to pay on the loan amount, notary and registry fees are halved and instead of paying the bank opening fee there is the subrogation fee to pay and this is a difference of 0.5% (normally bank commission is generally 1%).
I agree that if you have appointed a company to arrange your mortgage they should find the best product, for your circumstances and requirements, having discussed this at length with you. I have seen it mentioned that CFP have a limited amount of lenders on their panel so it may be the case that they cannot offer you the best mortgage. If you have been living and working in Kenya for some time therefore do not have a credit history in the UK then is it going to be more difficult for you as just about every lender will carry out a credit check on applicants to see what financial commitments they have and how they are paid and this assists them in determining whether the clients meet with their criteria. In fact criteria has got a lot tighter now as there are so many repossesions occuring due to initial oversight on affordability.
There is actually still a Self Cert product available in Spain BUT it is to a max of 50% LTV and limited to €120,000 euros.
Hope all above helps!