Garlic, onion and marigolds are all meant to help – so try planting your carrots in rows between lots of these.
This takes forward planning though! Although you can buy marigolds as garden ready plants and pop them in.
Sow thinly so you don’t have to thin out the carrots – this avoids creating any carrot smell which attracts them.
Plant in tubs high up. Get plenty of sandy soil and good drainage but water often and feed. This is supposed to work because carrot fly won’t fly over a certain height. Some experienced allotmenters think this is nonsense. Sow them thinly by mixing the carrot seed with dry sand and sprinkling this into the prepared seed drills.
and sprinkle that in the drills

Some species are supposed to be much more resistant to carrot fly. Some farmers plant after a certain date in Spring to miss the carrot fly which happens in two lots – spring and autumn. By careful planting in theory you could miss them entirely.
Barrier methods might also work – fleece stapled to canes around the bed can help.

Jersey Plants Direct have these carrot seeds available.

Carrot Flyaway F1 500 Seeds £2.99
natural sweet & British bredThis variety is a popular, naturally sweet, British bred carrot.

Carrot Amsterdam 1000 Seeds £2.99
Small and SweetSmall sweet carrots.

Carrot Autumn King 1000 Seeds £2.99
A large rooted carrot ideal for storingSowing time is from January to AprilThis variety of carrot has large roots and is ideal for storing