Blair/Brown Labour also had 13 years with large majorities and no angry backbenchers to (fully) legalize gay marriage, y'know...
They legalized civil unions, and would probably have legalized gay marriage if they'd won in 2010.
Therefore making them... the same as Cameron! (Complete with the "probably" - certainly a low level of probability given the previous 13 years...). Also still makes them more socially-conservative than John Lynch (y'know, that NH governor who's vetoing the medical marijuana bill; he signed gay marriage back in '09).