Lowest I have personally seen was a friend who just went to their local registry office, paid for the forms, the registrars time etc and it came to around £200 I think. They wore smart clothes they already had and didn't have any kind of reception after it and that was that. My mum's wedding was low key - went to the registry office, got some pics taken and then had a pub grub meal at a local hotel with about 10 guests and all in all everything came to around £1,500 which includes photographer, cake, her dress and stepdad's suit as well as my bridesmaids dress which all in all, is cheap for a wedding but it was very tasteful and you would have thought it would have cost a lot more.
I plan to spend roughly the same amount as my mum did for my upcoming wedding. There's ways to cut costs when it comes to wedding and any little you can save can make a difference. I'd never spend more than £5,000 on a wedding and even then, I would grudge it just for one day. I'd rather put that money towards something me and my partner would get a use out of every day or at least more than just one day like doing the house up, get a new car, go on a trip. Its the marriage that truly counts and that can be done with a cheap or expensive wedding.
You can save money on weddings such as - avoid getting married at the weekend or in the summer (those are peak times and will cost more), you can get really nice wedding dresses on ebay or amazon for quite cheap and a lot of them are actually really good quality, only invite a small group of friends and family, get cheap wedding bands from a jewelers such as Warren James.