This is exactly what I'm worried about. However, it is worth pointing out I always have an emergency stash of rainy day money, so when my tax bill is due at the end of Jan I would be able to get the money in the event of a drop in any investment account.
The tax bill isn't massive (around £3k). However, you are both right, any big drop in December would cause problems for me.
Jusrt seems a shame to have £4k or so sat around not working for me at all, just waiting to pay the tax man.
The Marcus account with Goldman Sach is a good shout.
I'll chew over it.
Thanks for your replies.