Beginner here so excuse the simplicity of the question. Just after reassurance
I am self-employed in the UK. I save money all year to pay tax in Jan. Is it normal to put this in a Cash ISA (w/trading 212) in the meantime?
I am nervous about how complicated it will be to withdraw when the time comes.
I can’t give you info about what folks do with money intended for paying tax but the withdrawal process has been smooth in my experience. My partner was able to withdraw money instantly from her cash ISA to her bank account.
Cash was transferred to her ISA initially via bank transfer (truelayer) so not sure if that might had an impact on the speed.
Thank you for this. From everything I’ve read it is supposed to be straight forward. I have linked my HSBC account so this should make it easier. 
I’ve had a mixture with sums up to say 5 figures. Some of it’s practically instant, on occasions it’s been an hour, or next day.
For me I just wouldn’t leave it to last minute, I think they say ‘may take up to 3-4 days’. You would just be unlucky if the withdrawal triggers a random spot check on your account so it might be delayed.
Great thanks for the reply. I’ve transfered it over now and will withdraw a couple of weeks in advance to be safe. Will be good to catch the last month of 5.17% 
Why not do a trial withdrawal to your bank account now, just to get a sense of what’s what and what to expect later.
The ISA is flexible so there’s nothing to stop you moving a lump of cash back and forth intra-day as far as I’m aware.
Good point, i should do that
ISAs have limited allowance per financial year. If you don’t mind using your allowance for only this small short term gain, you can definitely keep your tax money inside ISA until 3-5 days before you pay your tax in January.
Just be a bit careful with this though. Unfortunately I’ve found, and so have others on the forum, that withdrawing small amounts will be within a day but larger amounts can often take longer. So the £1 you test your withdrawal with may behave differently to when you want to withdraw £1k.
I think it also depends where the withdrawal comes from. US trades now settle T+1 for example but much of the world is still T+2 or longer. Cash ISA it should really depend on the method and counterparties involved.
I regularly withdraw/deposit amounts 10K+ the withdrawal time does not depend on the amount. Recently(may be like 3-4 months?) it’s almost instant. Having said that the max I’ve withdrawn is 35K and may be there are additional checks at 6 figures.
One caveat like @Dougal1984 mentioned is settlement times differ between countries, can even differ from one exchange to other. T+24h is very common and in several cases T+48h
So if you “just” made a stock sale in NYEX and asked to withdraw your money 1minute after that, your money is not actually in your account yet and will likely take 24h+
but in any case the OP does not sound like time constrained at all, and he is happy to withdraw days before, so this is kind of orthogonal to main discussion.
Thank all for the advice, as kali says I don’t have too much of a time constraint. It was just if there was something I missed where it could take months. Lots of helpful information here, much appreciated!
Hasn’t the rate changed to 4.9% ?