I don’t really think there are any.
My approach:
First thing to do is confirm whether the director has any shares. They usually do but not always. If not that is the end of the story from a capital point of view
If yes, decide whether the director is also “working” for the company.
Just being a director does not mean so although you can probably take it that they are if there is only 1 director. If they are you can disregard under 49(5) but you may want to have a look at treating any undistributed profits/excessive reserves etc as notional capital and/or notional income (but only if your claimant has >50% of the shares).
If you come down to valuing it…
You can capitalise the annual income (if the income is almost entirely generated from the capital of the company).
Take the book capital value but remember you wil have to make adjustments for goodwill etc etc etc.
Or type in =RND() into a spreadsheet and move the decimal point an appropriate number of places to the right. Works for me every time!