Barnet Market is now hosting a Sunday car boot and collectors sale. I was just passing by and popped in. It's on the site of Barnet Market in St Alban's Road, is on hard standing (tarmac) and will be open year round. It opens from 7 am until 2 pm and pitches, if you're looking to sell, start from £10, so if you're in Barnet High St on a Sunday why not pop round, free entry for buyers. You never know what you may find!
Unfortunately apparently the council isn't allowing sale day only local advertising (placards) so please help to spread the word.