not a better answer, but different[also belated]. Try any of the small chain of Tas restaurants-all are very attractive, staff are delightful and the food is both delicious and reasonable.Check their website for location; prettiest of all is Ev with a bar, cafe and deli attached. Great for vegetarians as well as carnivores.

i am assuming you will want a bottle of wine, so that leaves about £23 between you, including bread etc. Unless you fancy taking her/him? to a chain restaurant, your best option is going to a really lovely place where you can opt to sit at the bar and basically have bar food with a really nice bottle of red or white. One of my favourite places is Moro in Exmouth market in Clerkenwell, where you can sit at the lovely bar and order tapas. You can't book bar seats so get there before 7pm and nab two stools. The staff are charming, the tapas is great and you will sit there in the knowledge that you are in one of Britain's best and most original restaurants. £40? It's a bargain!