The website of the national archives holds many millions of digitised records from censuses to railway workers records, there’s a huge amount of data they hold.
You can do worse than starting at the National Archives website.
The site is a little cluttered which does make searching for your ancestor that much harder, but cdonsidering the amount of data they have it’s hardly suprising.
Only one real negative, you have to pay for each record you wish to see individually which could be very expensive if you’re not exactly sure of your ancestors details.
That said, they have more data than anyone else and a lot of collections that others don’t have, so a good place to start.