Most census sites charge for access. I'd assumed you'd gone down this route already, as it tends to be the most effective means of tracing people and one of the first things most researchers do.
You can access 1841-1901 censuses at
http://genesreunited.co.uk/ on a "pay per view" basis, or
http://www.ancestry.co.uk with a subscription. You can also access some of these free at
http://www.freecen.org.uk/ but unless you happen to be searching in one of the areas where there's 100% coverage, you're likely to need a paid subscription. The 1881 census is also available free at
http://www.familysearch.orgThat said, a subscription will allow you to gain far more information and may well take you back a couple of generations for the same cost as a single birth certificate.
Dominic