Insurance.
Try Stuart Collins and Co European Motor Insurance and Annual Green Cards
They are specialists in this sort of thing. If you have difficulties, come back to me via PM. The owner is a personal friend and will try harder!

MOT.
The test station can be anywhere - not necessarily close to your home. Just ensure you are reasonably 'en route' in terms of road usage and time. You are allowed to stop for rest (home overnight?) on your way. After the test you are permited to return literally anywhere. If it has failed, you can later use the vehicle to take it to/from any pre-booked place of repair. All withour tax.

Ensure the test is pre-booked, have proof of entry to UK (loading pass etc) and just get on with your journey. Just as I did a few months ago with an untaxed (by a few days) car with a long expired MOT.

SORN.
As you will have read, the vehicle has to be in the UK to be declared SORN. DVLA now acknowledge there is an anomoly in the Law, but are not sympathetic - they prefer to apply the letter of the Law rather than the spirit and try to extort informal Penalty Charges to supplement their Budget.
This is a separate topic away from this forum. Sufficient to say that at present I am part of an action 'against' DVLA through the Parliamentary Commons Committees, which hopefully will lead to a change of attitude.

Off Topic
You, like me, presumably have grown to love the personal freedoms of Russia and its CIS neighbours. I only go back to over-regulated, over-watched, over-restricted, over-taxed, rip-off Britain to see my family, enjoy proper and my 'local' pub life from time to time.

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