There's a K-r in stock at LCE Exeter, about 20 miles away. Just £120.
https://www.lcegroup.co.uk/Used/Pentax-K-R-+-18-55mm-F3.5-5.6-AL_242461.html

There's also Jessops in Exeter so maybe you can pick up a K-1 there if you prefer that, but they may have to get it delivered to the store so phone them to check on that.
Jessops: Exeter
Tel: 01392 436383
235 High Street,Exeter,EX4 3NZ,United Kingdom

https://www.jessops.com/cameras/digital-slr-cameras/pentax

There's also a London Camera Exchange in Exeter.

174 Fore Street
Exeter
Devon
EX4 3AX

tel: 01392 279024
They're he nearest photo dealer to you.

Try cleaning the battery contacts and check the battery is charged. It wouldn't be the first time I've inserted a battery upside down which didn't help make it work either! It's easy to forget something basic and panic when in unfamiliar territory.

Where you are does have a postcode (TQ13 7UB) so Post Office do deliver there. SRS can send by special delivery so if they get it in the post tonight it should be with you by 1pm tomorrow.

Is this a card that you've used in the camera before or a new larger capacity one?
If it's a new high capacity card it won't be compatible so find an old low capacity card and try that (up to 2GB.) If you're on the original firmware the maximum capacity card it can use is 2GB. However if you can get a card recognised, update the camera firmware to version 1.02 which will then allow the use of SDHC cards which come in 4GB, 8GB and 16GB sizes.
Sometimes a default setting can help clear issues too.

Try it using https://www.parcel2go.com/prohibited-items
Price should be similar and no restriction on camera items other than with Hermes.

Here is a link to the parcel force restricted items list:
https://www.parcelforce.com/help-and-advice/sending/prohibitions-and-restriction...
There's no mention of lenses in it, just digital cameras where the battery is not connected to the device.
Have you a link to where it says lenses can't be sent?

That Pentax 200mm will be better than the Tamron. Not because the Tamron is a bad lens but the Adaptall adaptors can lead to inconsistently exposed images. They were designed a long time before DSLRs arrived on the scene!
When you get your new lens have a good visual inspection of it to make sure the lens elements don't look cloudy due to fungus, oil or excessive dust. It was described as being free of those so check that it is. Also check that the lever that closes the aperture returns quickly. If it's sluggish it will lead to over exposed images and would require servicing to fix.

So how are you getting on and which Pentax are you using? Are you going to show us some of your photos soon? The only photo I can see you've uploaded is the one showing the time stamp you advertise in your signature! Surely you've taken some more since?
I notice on the Photography Review web site you say your first camera was a Nikon D3300. Did you swap brands?

Another vote for the M series 200mm f4


One of my first Pentax DSLR photos (K100D) from June 2009 of a tree sparrow (taken through a window).

I agree with the suggestion that the lens needs a K mount Adaptall adapter
eg https://www.ebay.co.uk/itm/Official-TAMRON-JAPAN-Adaptall-adapter-Pentax-K-PK-A-...
This one will work with the in camera aperture setting

or this one https://www.ebay.co.uk/itm/Official-TAMRON-JAPAN-Adaptall-2-adapter-Pentax-K-PK-...
which will be fully manual (green button stop down metering.)