If you are flying from EGKA to EGHS is there anything wrong in nominating the departure airfield as the alternate? So if Bournemouth is closed due to weather or a blocked runway, you just turn around, and fly the 30 minutes home where you know the weather will be ok to land? That is what I'd do anyway.
In a TB20 full of fuel you could divert to any airfield in England so you could put down Newcastle as your alternate if you wanted, or pick one on the fly if alternate 1 is closed,
The 170A is a load of utter bollox in my humble opinion, and I have never come across anywhere where you have to pass a test to be allowed to do a test!