Am surprised that you found such high prices. Current price for a Pakboat Quest 150 in the US is around $1350 which translates to about 1000 quid. Shipping would only be around $300 (my brother, who reconditions vintage drum sets, just shipped a large drum from upstate NY to Manchester UK for that much and the package was about the size and weight of a bagged Pakboat.) If you found a used folder in the US that somebody was willing to box to ship I think you could get a better price than what you found. From what I understand "canoeing" (which in the UK includes kayaks) are exempt as sporting goods from the VAT.
https://www.gov.uk/guidance/sport-suppl ... tice-70145
I would caution you on considering boats like the Innova Safari for your intended usage. Coastal paddling in Britain is in serious waters where you need to consider tides, rip currents, offshore winds and quite cold water year round. Open boats, especially inflatables, have drawbacks for such conditions. They are susceptible to being blown around by wind due to the bulk of the tube walls, this also can make them very difficult to control and to propel forward in rough water. The chances of being swept off shore beyond where you can easily regain land under your own power are a concern. Also, open boats are a wet ride and you would be exposed to the water at all times -- paddling such boats in the seas around the UK would require temperature protective clothing like wetsuits and/or drysuits.
If you want to limit your paddling to inland rivers and lakes, the inflatables you are looking at will be OK (though still with the proviso of possible problems on large windy lakes.)
A better option would be to seek a used boat, so that you can get something more suitable within your budget.
You might consider contacting Pakboats (not Pakrafts -- that is a different animal). They are a small company and they are very good about personally responding to inquiries. They sometimes have used boats and demos for sale and in some cases have had information about some of their boats available overseas from dealers or outfitters.
You might also be able to find used Folbots, Kleppers, Pioniers, Nautiraid, Wayland, Longhaul or the other European made folding kayaks for sale. Folders have long been more widely used and distributed in Europe than in the US.
There is a UK dealer that often has used boats available for sale:
https://www.foldingkayaks.co.uk/folding ... ntage.html
PS: found this Wayland for sale on Ebay in Salisbury, starting at 800 quid or "best offer". Try offering 600 and see if they bite. Listing is only for another couple of days:
https://www.ebay.co.uk/itm/Kayak-Waylan ... rk:19:pf:0
PPS: Just learned (from a forum post on here) of another folding kayak brand that is available in the UK: Neris. They are located in Reading. Here is the model and price list. Their Valkure 1 is 1060 quid (extra for spray deck, which you would want.):