Insurance is a legal requirement ...
Public liability insurance, quite rightly, is a statutory requirement on all markets, anywhere in the UK.
Full Public Liability Insurance cover is provided FREE by joining the National Market Traders Federation
(see link). http://www.nmtf.co.uk/index.php?id_cpg=6
As an alternative, you can also obtain Public Liability insurance for a premium of £55 per year by contacting; G M Imber & Sons Ltd http://www.gmimberltd.com/MarketInsure%20Starter.html
or downloading their proposal form
Finally another one to try is: http://www.lroinsurance.co.uk/sections/what/retail.html