Thanks again for all the considered comments. Needless to say, I won't be dealing with this shop again.

David, Chris, Andy, I do take the point about giving the seller reason for complaint about receiving the gun disassembled. With hindsight of course I should have sent the rifle back in one piece just to avoid the reaction I got!

Interestingly the Office of Fair Trading's notes on distance selling address the issue of packaging and the right to examine goods. In breach of the regs, the shop didn't publish any terms or conditions whatsoever on its website, or inform me what they were any other way.

Here's the OFT's section on cancellation rights and returns to help anyone else who finds themselves in a similar position (my highlights).

• unless cancellation rights under the Distance Selling
Regulations ('DSRs') do not apply, you must provide clear
information on cancellation rights and how customers can
cancel an order. Generally consumers have a minimum of
seven working days commencing the day following delivery
to exercise cancellation rights

• if your customer wishes to cancel the order, they must take
reasonable care of the product while in their possession

• you may set out what you consider to be reasonable care but
you may not impose conditions which prevent your
customers from exercising their right reasonably to examine
the goods. Typical conditions which may breach consumers'
rights include requirements that goods are returned unopened
(except in the case of sealed software or audio/video
recordings), 'as new' or 'in their original packaging'

• if the customer cancels an order under the DSRs, you may
not deduct from the refund the costs of outward delivery nor
other fees, such as an administration or restocking fee. The
refund should be made as quickly as possible and within a
maximum of 30 days

• if you wish to require your customer to return the goods in
the event of cancellation and to pay for the cost of doing so,
you must make this clear in your terms and conditions and
confirm it in writing or another durable medium.