I have a small garden in which I'm trying to grow a selection of veg (in a very small part of it). I think I've discounted the idea of a compast bin as it would take up so much space but what are the advantages of a wormery over a compost? Is there any point of getting either for such a small garden?

I would say it is always a good idea to compost if you can. Not only is it good for the garden but it cuts down quite a bit in your refuse bin.
Even those who only have a balcony can compost if you use one of the Bokashi Kitchen bins.

A wormery is good for not only the resulting compost, but the liquid you can draw off certain models is a fantastic feed for your plants (watered down)

"With a Bokashi system, you can turn your food scraps, including meat, fish and dairy, into rich compost. Add your kitchen waste and a handful of bokashi bran to the airtight container and allow the micro-organisms to work their magic. After two weeks the contents can be safely transferred to your compost bin or dug into the garden." (http://www.leangreenhome.co.uk/bokashi/bokashi-explained/)

From my understanding, standard composting is a slow process - it's quicker in the summer but still takes about a year as you'll never get enough heat from the decomposition to get organisms like thermalites working to breakdown the organic matter.

A worm farm, on the other hand, will create good usable compost much more quickly. Worms breakdown the organic material and you help to keep the mixture well aerated by turning it regularly. The worm casts are a very good ingredient, apparently.

The composting process is not an easy one to get right, from my experience. The mixture needs to have the right proportions or nitrogen-rich and carbon-rich matter and also moisture and air content to avoid anaerobic decomposition.

By the way, I'm not an expert so please correct me if anything I've said is not right