I am ex Bank and agree with Bubblebunny in that all lenders vary considerably in what they will offer. To be honest the calculators on the websites are very crude approximations, and should not be relied upon at all as being accurate.
Most lenders now utilise net income ratios in assessing how much they will lend. Factors such as no other loans, maximum loan term, factorment of mortgage interest relief, and various other factors can increase the amount which you will qualify for. In addtion to this many lenders will offer larger amounts to many civil service employees or applicants who are willing to accept a 3 or 5 year fixed rate.
I whole heartedly agree with the attitude of only borrow what u can afford as opposed to what you can get approved for. This is most prudent.