Get a rocket blower from Jessops or L.C.E. in town, take the lens off, hold it with the front down towards the floor and blow away. Just make sure you don't hit anything inside with the tip of the blower. I'm sure if you take it into either of the shops in town and buy a blower they'd probably show you how to do it by doing it for you. It's about a 10 second job. Alternatively, as you live in Lincoln and I only live in Branston, about 4 miles away, you could bring it here and I'd do it for you. I think I've even got a spare blower you could have. PM me if you want to bring it.