If you`ve always wanted to try Dom (and the bottle we had was exquisite - probably because we weren't expecting it) I would buy it and drink it at home. I wouldn't pay the massive mark up that the restaurant will add.
I did think about doing that, 237, but there's only a £33 price difference between what the restaurant are selling it for and what I can buy it for online.
Frankly I think Champagne is vastly over-rated especially with the UK restaurant mark-up. I'm just as happy with a sparkling Loire - our favourite is Veuve Amiot for about 5 Euros (though I don't think you can buy it in the UK). We always stock up when in France.
I agree Diddly, a nice Methode Champenoise or Cremant is much more drinkable than Champagne and much more reasonably priced. My French neighbours do not buy Champagne.
I drink gallons of prosecco but I buy it directly from Italy and it bears little resemblance to the stuff in the supermarkets in the UK. Its less fizzy for a start.
Yesterday I went out to lunch with some friends. I only had a glass of rose wine but some of the others bought a bottle of Cava. It cost £30 and a bottle in the supermarket is about £9 (it was a Reserve). Apparently, there is more of a mark up on cheapo wines in restaurants than there is on more expensive bottles so it's sometimes better to have the expensive ones.