Im an american visiting family abroad can i book a round trip ticket to london from july 2011 to april 2012?

I need help :o( I am planning on leaving in a few weeks to london. I am visiting family throughout Europe and visiting Qatar. My question is can i book a round trip ticket to leave the US for london in july 2011 and return in april of 2012? I plan on being in london for 3 months then traveling to Qatar for 3 month then return to Amsterdam for 3 additional months to base my self there while i visit other family throughout europe and return to london to head back to the US. Which means i will not be returning to the us till April. I am only booking my round trip ticket to london and from london. Can i do that?????? I don't have exact dates for my trip to Qatar therefore i will book that ticket once i get to london..... Will i have any problems entering london if my only proof of a return ticket is for nine month away (july to april)??????