Ancestry has added a new collection of records from London's Clandestine Marriage and Baptism Registers, 1667-1754. It's a sizeable oollection, holding 894,892 entries, and it's both searchable and browseable.
If you follow the link above, you'll find an explanation on of the term 'clandestine' in this context, and you can be sure there's a good number of Irish within the collection.
Moving swiftly forward a century or two, don't forget that Ancestry is currently offering free access to the 1911 Census for England and Wales.
You have to register with name and email, but there's no requirement to provide credit card details.