Beaconsfield Pickleball Club supports the initiative of a British company - www.pickle-ball.co.uk - which stocks paddles, balls and other equipment. The owners are pickleball players themselves and are dedicated to growing the sport and the player base. 

An alternative is; Pickleball Portal: 
https://www.pickleballportal.com/gear​

Personal import of equipment from the U.S. may seem like a good idea.  However, prices quoted on sites – including Amazon – often do not disclose that, in addition to carriage, Customs Duty and VAT are payable on the goods on entry to the U.K.  These charges can almost double the listed price of the goods.