I'm a controller, not at Heathrow, If you keep getting a late clearance its probably the cotroller working their little socks off to make sure that they deal with as many aircraft as possible. We try to get it right as much as poss and occasionally you might get a go-around but the only alternative is increased spacing which give reduced landing rates which the BAA aren't going to like.
Just rest assured that the controllers are trying their best for you and if you do go around well its better than hitting whatever is on the runway.....
drink beer smerk tabs...