Of the 2, I'd go option b.
What about:
(C) company contributes to a pension. Growth tax free within fund, and generally speaking once you're not employed by that company when you reach 55 you can access the pension.
Re: option a
It's usually a bad idea to leave funds within a company like this. The company pay's tax on undistributed profits, and capital gains / income tax on any return. You then pay tax when you eventually take the money out.
With forestery, returns are tax free so you might as well invest directly.
You mention 100k investment. Spend a few hundred quid on professional tax advice. It'll pay for itself multiple times with an investment that size!