Thanks all for your comments and advice. As I say I know it's a contentious issue and raises a lot of strong feelings for some people, but I asked for opinions so that's fine, and everyone is entitled to their views. 
Oddly I started looking pregnant very early on, (undoubtedly bloating rather than baby I know, but still gave the game away to the point that work colleagues guessed when I was only 10 weeks), and particularly by the evening most days I look more like 5 months than 3, so yes I do think someone would realise I was pregnant if they saw me in a restaurant of an evening. The general consensus from here and other people I've spoken to is that yes, a small amount of alcohol occasionally should be fine, especially once past the first trimester, so I think that's probably what I'll do. I probably won't even have a drink every week, but it's nice to have one occasionally, especially if out for dinner for a treat or similar, or if it's a special occasion.
It is difficult though to know where to draw the line on 'risk' especially as there's a lot of conflicting advice and people with very strong opinions. I've been on Mumsnet for a little while now and I've heard people say that they wouldn't do the following during pregnancy:
- Go in a car, unless absolutely essential, in case of the risk of being in an accident.
- Eat in a restaurant / get a take-away because they wouldn't know how their food was prepared.
- Go on a plane, even for a short-haul flight, in case they got DVT.
- Drink a cup of tea (even one cup a day) because it contains some caffeine.
I am doing all of the above still, so I guess I must be a terrible mother-to-be in the eyes of some people, but as much as I of course want this baby to be born healthy, I also feel that I have to keep on living as normal a life as possible in the meanwhile, and that it is possible to get a bit excessively risk-adverse during pregnancy. But as I say, it's hard to know where the 'line' is sometimes.
Thank you to everyone for their comments. I appreciate the honest feedback. 