Before you attempt anything check with your local council office they may have an assistance scheme of re-roofing older properties under the 'energy saving' title start with planning if it's not them they will direct you to the relevant department, it's worth the cost of a call.
Tile breaks are not easy to spot on interlocking tiles but are easier to spot on the plain flat ones. look in the loft when it's raining and note where the rain comes in it is most likely some where on that line up the roof. Also if you have gable roof then it could also be the valley flashing. Some pictures might help email them to robertwhiting76@hotmail.com and I'll take a look and see if I can spot anything. Try the council first you may be suprised and they might cover 2/3rds of cost for either sealing or re-roofing.
Nobby
February 2008