Because of the Contracts (Rights of Third Parties) Act the matter is purely contractual whoever you proceed against. Proceeding in tort is far more difficult than contract. To a great extent contractual liabilities pretty strict whereas tortious liability is much more difficult to establish.
Also, as I have suggested – going against Crampton will put them in conflict with Arrow – no bad thing.
Crampton, telling the OP to go against Arrow – is a bit like Currys or PC World telling the customer to complain to Lenovo. It simply passing the buck. Much better that you keep the dispute with the retailer and then it's up to them to complain to their service provider or their own supplier. That leads to an overall improvement in standards by both parties. If you simply proceed against Arrow, then Crampton will never care whether their delivery agents cause damage or not because it won't be the responsibility.
If it is not possible to repair the frame, then Crampton will simply have to cough up for a replacement – and if they refuse then a court will force the issue. Then it's up to Crampton to take it up with Arrow.
On a practical note, if you ask any UPVC door/window supplier about the cost to repair, they are more likely to say that's not possible and will quote to replace the door and frame. Depending on the door size and adjacent windows, the cost could be £1,000+ which may be disproportionate, depending on the damage caused.
However, if you search the Web for UPVCdoor frame repairs, you will find specialists that should be able to quote to repair. I would expect the price of this to far lower.
I'm probably being dim, but wouldn't it be more straightforward to proceed against the courier who actually directly caused the damage rather than the retailer? Isn't this really a question of negligence and tortious liability on the part of the courier rather than anything to do with a contractual relationship (to which the OP may or may not be a party)?
The OP is saying that the damage to the freezer has been resolved with the supplier, and I'm really struggling to see how any liability the supplier may have extends to damage caused to the OP's property by a third party courier.
The damage is presumably blatantly obvious (and quite expensive if a PVC frame) and clearly caused by the third party, not the retailer. I'm not saying that claiming against the retailer is not the way to go - I'm just saying that in the OP's shoes I'd be claiming from the courier, not the retailer.
(The only practical advantage I see of claiming against the retailer is that they'd be more likely not to use this courier again - but I don't think a third-party claim against the retailer is as clear cut as claiming off the courier).