Sussex appears to be a county with prentions! Not only is it split for administrative purposes into two (a bit like Yorkshire) it also claims three flags (unlike Yorkshire)

They all feature  a mythical bird called Martlets which have been long associated with Sussex.

The County Council do offer a flag for sale, which presumably is licensed to them: You can buy them form their site here a snip at £36!

Alternatively the England Store offer these versions for £4.99.

The Sussex flag was recently unveiled after being designed by teenager Brady Ellis, see the article here

The Sussex flag

East Sussex flag

 The West Sussex flag