the kite mark is minimum standard make sure it is the up-to-date on with the 20mm bolt. this is BS 3621-2004
I've found ones that go rusty inside or suffer from broken springs are the cheap brands, so I always use Chubb (which also have a 15-year guarantee), but I'm sure there are other good brands. It should cost you less than £25 (don't believe RRP).
Apart from your Final Exit door (last one you lock when you leave the house), back doors should be supplemented with bolts, preferably the mortice rack bolts with a removable key.
If you have a nightlatch on your front door as well as a mortice deadlock, it is best to have one of them a third down from the top, and the other a third up from the bottom. Gives best strength against shoulder or kicks.
If you can have a small but solid keysafe to put your spare keys in, anyone who gets into the house (e.g. through a window) will then not be able to open a door and walk out carrying all your belongings, but will have to climb back out through a window, carrying less.
Don't leave keys in locks, or on the hall table within six feet of the letter box, even if you are at home.
Consider the security of al your doors and windows, since a burglar is under no obligation to attack the most secure one.