Tax breaks
I've been out of the house rental game for a couple of years but I used to claim the following:
Management Agency Fees
10% of wear & tear (or replacement costs for carpets etc)
Cost of visits (fuel etc)
Stationery and postage
Mortgage (treat it as a business, then you can claim this as an expense)
Basically, anything it cost you to run your rental you can claim back - it's possible to pay no tax, and even carry a loss forward.
The one thing you do have to be aware of is potential future liability for Capital Gains - Inland Revenue tried to get me on that with a £20000 payback, plus a similar sized "fine". Just be aware - but it only cost me £385 for a tax consultant to fix the problem!
Good luck!