This is something I came across recently and it might appeal, This is the last Paddle Steamer in the UK and you can hire it for your wedding reception. It is called the SS Waverley and it operates all round the British coast.
If you are interested go to www.misses-2-mrs.co.uk and they are wedding planners and they organise weddings on this boat along with all sorts of other things. They are based in Gretna Green so thats a green venue.
Alternatively you could contact www.waverleyexcursions.co.uk and then you can see lots more pictures of this great boat and find out more about what they offer.

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Le Manoir aux Quat' Saisons

Now this is a really special venue, and it is quite green. My Daughter and Son in Law bought us a meal for two at this restaurant as a thank you for their wedding. What a nice gesture and something all you Brides to be could bear in mind. It does not have to be at Raymond Blanc's establishment, though it would be a good choice and it does not have to be a meal out, but a little thankyou will I am sure be appreciated.
You could have your wedding reception at Le Manoir, it is a green venue in that they have extensive gardens, very beautiful, but also a very interesting vegetable plot, which supplies the kitchens. So no transport involved and all the vegetables and herbs are as fresh as you can get. Also you eat seasonal food (thus Quat' Saisons)
If you do ever eat there then do try to have a look at the gardens as they are almost as good as the food. Particularly because they grow some interesting veg, such as Salsify and Scorzonera and Chard, to name just a few.
It does cost quite a lot, but as I said my visit was paid for, however I would not say it is expensive as that suggests you are paying too much for what you get. It is not simply a meal it is an experience of the very highest standards of cuisine, service and suroundings.
Have a look at the web site www.manoir.com and start saving up.