Hi Nicola, you'll most likely find that Ancestry.co.uk, and Findmypast have a 14 day free trial so you can get started without paying.
If you organise yourself first with all the information you've already got to hand, it's amazing how far you can get in 14 days. I don't think the 1911 census is included in the free trial though - in fact it's not yet on Ancestry.
I started on Ancestry's free trial - then at the end of the 14 days, my sister and I clubbed together for a year's subscription and have done so ever since.
Through that site we've made contact with other distant family members and we've pooled information and photos. You can choose whether or not to make your tree public on Ancestry, but it helps when people do make them public, because when your relative pops up on another tree you can glean information from someone else.
Don't order BMD certificates through them though. It's cheaper to do it direct if you can get the information first.
Happy hunting!