Gossipwitch, pagans are on par with just about every other religion. Hindus, Muslims, Sikhs, Humanists and Jews also need to have a separate legal ceremony held in accordance with Civil Law. The full information is here: www.weddingguideuk.com/articles/legal/englandwales.asp
For non Civil/CofE marriages, the actual legal part of the marriage is conducted when the couple sign the Register and say the required words - the wedding ceremony/religious celebration is not the legal marriage. Interestingly Civil Law prevents ministers of religion becoming Registrars, and there is also no alcohol allowed in rooms which are licensed for weddings. The main reason that there are no licensed pagan venues is because there are not many indoor pagan venues, and a licensed premises has to have a roof and some walls. Most handfastings are held outdoors in places far more beautiful than any room.
Although it would be lovely if I could legally marry people anywhere (can't wait for the law to change so that Stonehenge handfastings become legal!), at the moment the law does give pagans a huge amount of freedom. Okay, you may have to do the legal bit at the Registry office, but you only need two witnesses, the couple and the Registrar, and to say two sentences and you are legally married.
You can hold a handfasting absolutely anywhere you like, at any time you like, say anything you want to say, wear what you want to wear, involve who you want to involve and, if you are pagan, spiritually this is the most important bit because you are making your vows to each other before what you hold sacred, so you can call upon any Gods that you want to call upon.
The system isn't perfect, but it's not that bad, and the fact that the handfasting isn't legally binding, has never dampened any enthusiasm or celebration for the hundreds of couples we've handfasted.