Usually the number is in a triangle.
Find out which your council do. They can recycle most plastics, but some cost around £1500 per ton to turn them into useful material, so they often don't. As recycling becomes more popular, then the costs should come down, so that in a few years they will be able to deal with more types of plastic.
You could check with whoever makes the yoghurt pots as to what the symbol means too(they should have a website) and while you are checking, tell them that you will pay a bit more for yoghurt if it is in a recyclable pot (It helps to keep encouraging them to think about it)
HTH