They have been cut from circulation - that being said, an old style 10p is worth more than face. And yes, you can still try to spend them, but its the discretion of the person taking the money - however, as soon as it is spent, it will go straight out of circulation, and probably into that person's pocket. But they dont have to take it, and a lot of people will probably think you are trying to trick them with a fake.
Basically, dont spend them, they arent proper money, but try and spend them and you probably wont have too much trouble with it. The 5p is the easiest because its the same size(ish) as the new style 10p, and you still get some circulating disguised as 10p coins.
I say keep them. The old style coins are nice and chunky and the NEW PENCE is a nice bit of history for any collection.