However, it is possible to get higher mortgages if you are buyin a property which is need of renovation/modernising. This can be complicated and lenders are nervous if you are going for 110% mortgage as opposed to putting down say 40% of the asking price and asking for 60% + additional funds for the property.
I believe that the bank will not lend above the valuation price, as their interest is in being able to regain the money they lent you by selling the house (should you default on your repayments). However, you would be allowed to buy a house for a price over the valuation price as long as your deposit pays the difference and the loan amount still lies within the valuation of the property.