You’d need to factor in taxes and broker fees on that money also?
Not if it's in an ISA wrapper. Plus you get allowances which renew every year.
To use up an allowance all you need to do is sell your investment. Park that money for 30 days. Then on the following day re-buy it. You have to wait to the 30 days though otherwise it's not classes as selling it.
Or you can alternatively just sell it and invest into something else. Once the gain is realised is when the tax is due. So if you sell yearly and invest into something else and it's below the allowance for that year you pay nothing.
Technically you can do that within an ISA and you have an unlimited tax free allowance. So if you open a T212 ISA account and only put £20k cash into it per year then whatever you make is completely tax free.
That includes if you tripled your investment sold it and then invested in something else that doubled all within the same year. Just as a theoretical example.
So no if you are smart you can work the system to pay zero taxes.
I'd therefore personally say use your ISA for a T212 account and then use your tax free allowances up on your vanguard account which isn't in an ISA where profits are likely to be lower / less.
For example the best you can hope for with vanguard realistically is 10% a year. Whereas with T212 if you invest in the right companies at the right times you can realistically double or triple your money within a few months problem is I don't put all my eggs in one basket so I will have my investments spread out over 10-20 companies and one will hit 100% return over 3 months the others won't have hit anywhere near that bringing the average down considerably.
But if you did gamble it all on a lower number and one or two hit it big time it's a much better use of the ISA system.