The good news is they finally rang whilst I was writing this with
profuse apologies and a refund is on its way.

Thanks,

Andrew

Good news that its sorted. Was probably a simple mistake.

I guess this depends in the retailer, but I 'think' the contract is
formed when the retailer despatches the goods. Example from T&C from a
very well known online retailer (I've trimmed this):

'
Contract creation and electronic contracting

The technical steps required to create the contract between you and us
are as follows:

You place the order for your products on the web-site by pressing the
confirm order button at the end of the check-out process. You will be
guided through the process of placing an order by a series of simple
instructions on the web-site.
We will send to you an order acknowledgement email detailing the
products you have ordered. This is not an order confirmation or order
acceptance from x.
As your product is shipped from our warehouse we will send you a
despatch confirmation email.
Order acceptance and the completion of the contract between you and us
will take place on the despatch to you of the Products ordered unless
we have notified you that we do not accept your order or you have
cancelled it in accordance with the instructions in How to cancel your
order.
'

Will