Apologies for not replying for a couple of weeks, I've been busy in real-life.
I've had a rethink, trying to maximise the room that I have available and to avoid the traverser. I've come up with the following which I'd really like people's views on whether it works, and also any pointers or changes to make it operationally plausible.
I decided I can use the back wall of the garage too, giving me a maximum space of about 6000mm x 2010mm in an L-Shape. I wanted to keep it 2ft wide.
I'll have a 1829mm x 607mm board tucked into the top right as you look at it, so all the pointwork fits on one board.
I've managed to squeeze 3 x platforms that are long enough to accommodate the class 800 on my wishlist, as well as a shorter siding and bay platform, with nothing tighter than a 2nd radius curve (mostly less). The Hornby platforms are there just to help me visualise it.
If this works, it should give me enough length along the top wall to still have something of a layout and a hidden fiddle yard.
????