First post, so I hope I am in the right place!

This is one right place (we are a world-wide group).

Now, assuming you are in the UK, I can't very well blame drought. Not
this summer.

dwarf beans, potatoes and a couple of cabbages

In what manner did they die? Leaves brown? Yellow? Bits of the
leaves gone (which would mean something was chewing them)? Lack of
growth? A few of the possibilities a (1) fungal pathogens
(especially likely in a wet year), (2) insect damage (often possible
to spot the insects if you have been looking carefully), (3)
something, such as a toxin, nutrient deficiency, or too much of a
nutrient, in the soil/compost (can be hard to track down, but trying
different parts of the garden in different years might give some kind
of idea).

Careful observation and consulting with someone local to you who knows
what problems are common in your area can help. You can also try
posting photos (via flickr or some such service, not directly to the
group). We'd probably need to see what the plants looked like as they
began to sicken, not when they were completely dead.