Any ideas on where to get short-term insurance (3 weeks) for a camera worth around 500 GBP. It won’t be covered by household insurance & the best I have found via travel policies is 250 with a 250 excess. Camera insurance companies seem to sell annual policies which are kind of pricey.

i have m&s / axa home insurance with items away from home cover which covers items up to 4k £38 a month all in , bikes etc all covered

Speak to your house insurance people. They should be able to add it. Or, get an annual policy that allows you to cancel after a month.