hang on... uv filters do certain things... they dont just sit there and look pretty and protect it...
tbh if you drop a lense it probably will need to be re calibrated weather you think that it doesnt or not... u may drop a lens and take a shot and it will look fine, however there is probably some point in its focal range where it will be off!!! lenses DONT like being bounced! the lenses inside can shift... when assembled there is alot of time spent ensuring the internals are in perfect alignment... it doesnt take much to knock them out! so even though the filter may have saved you, i would still send it off to get it checked EVEN IF you have taken photos and they look fine!!!
uv filters should be used to cut down on uv lol, like if you go up a mountain and take photos do it with no uv filter and you will have a blue cast on your images, stick a uv on and it will cut out the blue cast.... but at sealevel there really isnt that much uv its pretty much scattered by the atmosphere...
at the same time you have to think... is sticking a £15 filter on the front of a £1000 lens really a good idea? i mean bet that £15 filter isnt anywhere near as clear as the end element on your lens lol... and its bound to reduce quality to a certain extent (weather you claim you can see a difference or not!!)
look at using a Tiffen 812 which is a slightly warming filter does a better job... or the 81b or a tiffen haze-1 and if u want a uv the hoya uv ones seem the best as cutting out uv from tests i have seen.
if you want a polarizer get a hoya circular polarizer