I Have maggots in my swede

Swedes are a brassica and it sounds like cabbage root fly grubs? As long as they haven't done too much damage just cut off the affected area!

it's probably cabbage root fly larvae.
they attack all brassicas (and my radishes).

you can still eat the swedes, just cut the damaged parts out

Thanks for the reply at least all is not lost. Is there anything I can do to stop them eating the rest in the ground?

Not really at this late stage, swedes being basically a swollen root are a bit harder to protect as you cannot use a brassica collar, for swedes use something like fleece, net curtains, enviromesh etc but this wont protect you from any lurgies in the ground. If you are able I wouldn't grow brassicas here for a few years, if this is not an option then turn the soil over at the end of this growing cycle in the hope that any soil pests are exposed for birds beetles etc, then use brassicas collars for above ground plants and mesh for swedes.

Cabbage Fly

The maggots you have come from the cabbage root fly, they are black flies with white stripes on their backs, they lay eggs in the soil near the stems of certain veggies like cabbage and swedes and turnips, the larva then hatch and burrow into your lovely organic veggies and feast till they turn into cocoons, you may find red cocoons in your soil.
There are many ways to stop them, one way is to wait until they fly breeding season is over normally around mid July to August and then sow your crops, this way any flies that do get into your soil will find nothing to eat and die, another method is to put fire ashes all over the top soil of your stems and around the plants, or you can cover the ground around your plants with very fine cheese cloth, this stops the flys laying their eggs.
If you wait until the end of the breeding season you will also be spared the hassle of moth eggs and butterflies as these also breed at the same time and will dine on your crops.
Pesticide is another method, but if you havent used it already then I would assume your looking into totally organic crops, like most people try to grow.
Unfortunatly organic crops are tasty for us and them, or you could choose sacrificial crops, you place certain crops near your other crops and hopefully the pests go for them instead.
Regards
Rob