Peas and wiggly things

That sounds like pea moth, the adults lay eggs at flowering time before the pods are formed and the maggots hatch out inside the pods and start eating.  The way around it is to cover the plants during the risk period with mesh to stop the adults laying the eggs.


Cawdor

You've got pea moth. And it will stay in your plot/yard. To avoid the problem, peas must be sown indoors from Jan to mid March (no later) as direct seeding will either rot or be at its most vulnerable during the worse of the caterpillar season.  By sowing them early indoors, the pea flowering occurs before mid June which ensures the pods will escape the worst of the pest. They live in cocoons in your soil over winter, pupate in spring and appear as small moths in summer.
So, this year you'll have to plant in a spot you've never planted peas in before, hopefully you've already started some, put them in and cover tightly with fleece on posts which keep the fleece from touching any leaves. Peas self pollinate. This fall you'll need to spade up your soil well to leave it exposed to the elements and predators. The caterpillars rarely attack mangetout as those are picked early when tender before the cateripillars emerge.

Sow yesterday, as said and again end of August, it's a summer pest, as again Tril said before.

Do that for a few seasons and fingers crossed.  Unless some folks around keep sowing summer peas....

They should be perfectly fine, it is a cool crop after all.