Right now parliament is debating allowing gay marriage, which is expected to pass. The legal ramifications seem to be negligible, just that calling gay marriages civil partnerships will stop, they will be carried out by the same people and same places as conventional marriages, and be called marriages. The rules allow many churches -only if they wish - to carry out same sex weddings. peculiarly the church of england is expressly excluded form being able to chooses to perform gay marriages should it wish.
After listening to the arguments a bit i am afraid opposition to this all comes do bias against gays. The practical changes are small, because partnerships are already legally recognised. There seems to be a big chunk of opposition to gays being allowed to say they are Married. Likewise, to churches being allowed to carry out such marriages. Surely this makes no difference to any church, which is simply allowed to do this if it wants.... unless some minority within the church is still fighting a rearguard action to stop that church accepting gay marriage, and is seeking to do this by keeping it illegal even though the majority in that church might wish it.
The conservative party has got itself into a complete knot on this. Conservatives have systematically opposed every reform allowing gay rights, only retrospectively embracing changes after thay have been forced upon them (by the public!), but always complaining about the next step. The british public wants equal rights for gays. Conservatives by a significant majority oppose this.
So it is even stranger that the conservative leader, David Cameron, has decided to force this through. Not least because he too has a long record of opposing all the reforms to provide gay rights. In opinion polls the public, by a wide majority, believes this is a cynical move to try to win some votes. Cameron's move, trying to demonstrate he represents the 'nice' party, is seriously undermined by MP afte MP from his party coming forward to denounce this. While at the same time he cannot possibly retreat, because that would be the final proof the whole party opposes gays.