While I've been doing this every time I go through Immigration to go back to London where I'm staying immigration keeps asking how long I'll be in London and review documents of my return flight and my bank account to confirm that I will not be using public funds or working illegally.
Um, actually right now, what you are doing is working illegally in the UK.
You cannot work in any capacity while you are visiting in the UK - this includes:
- working for a UK company
- working for a US company
- working for yourself
- working online
- unpaid work
- paid or unpaid volunteering
If you are here on a visitor visa, it is illegal for you to work for your US company in any capacity.
Is there any possibility that they will deny me entry as I tell them I'm simply a visitor? And is there something I can do so that I do not have to worry about getting denied entry?
First off, you can stop working. Completely.
If immigration find out you have been working, or that you intend to work on future visits, and that you have told them you are not working when you actually are, they can determine you are using deception to enter, which can lead to a 10-year ban from the UK.
Also, while there is no hard and fast rule about how long you can be in the UK as a visitor, if it looks like you are using the visitor visa to essentially live in the UK (which it sounds like you are), they can refuse you entry to the UK at any time.
The general rule of thumb to try to stick to would be to spend at least as much time outside the UK as you have just spent inside the UK before you try to come back... so if you spend 5 months here, you should spent at least 5 months back in the US before trying to return to the UK.