RE: The maths here21 Feb 2019 14:23
Well it depends what you do with the remaining 90k shares - keep them, sell them?
If, as a hypothetical example, you buy 100k then sell 90k at today's bid-offer spread 35.3, 36p (at the time of writing) and including dealing costs and stamp duty, sell 10k for 0.46p then I estimate you would make £166 profit!
The stamp duty takes a chunk (Ā£180 or 0.5%) and the spread. So whether you make a (decent) profit critically depends on what price you can get for the 90k ...
QF