many lenders these days opt for an affordability test, in which case net disposable income (taking other debts and income into consideration) is a core issue.
many otehrs dispense with stringent checks on expenditure at lower LTV's
Your best bet is to speak with a quality mortgage broker. Contrary to some opinion, you will get the best deal this way.
OFFICIALLY you can only be given a mortgage on an affordability basis. Yes the checks may be less stringent if you take a lower LTV but the lemder will still take a credit check - which will show them your debts. They are always taken into account. As norlo says a mortgage broker really is the best place to go. Even if they charge a fee - it will pay for itself.