Okay - think I understand what's happening now. It's referred to as a VIMBO - vendor initiated management buyout. The owner is selling the shares and the actual sale is funded by the company, probably by vendor loans (the seller loans the company the money to buy the shares from them). The following is a very broad explanation - in real life there's lots of ifs, buts, twists and turns! This might be a phenomenal opportunity or it might be a way to extract cash and dump problems on someone else so you need to go in with your eyes open.
This deal can be done in two ways :
All the shares are transferred at the outset. For example company valued at £1m. All the shares go to the individuals, and the company has a debt of £1m. There will usually be strict penalties and high interest to reflect the "risk" the seller is facing . (ie if the company performance dips and doesn't have the cash, they won't receive their repayments). There are also likely to be restrictions and vetoes imposed while the money is outstanding (eg new mgt team can't invest, borrow, acquire, hire someone over £50k or sell without vendor's approval). If this is the scenario then you are the owner from day 1.
2, Drip down - shares transferred in tranches eg 10% of shares every year for 10 years. You won't have control of the company until more than 50% passes from the seller to the management team. This is more unusual these days (because performance may fluctuate affecting share value and also exposes seller to higher risk. On the flip side they can benefit from upturn in performance)
The seller will have a price they want for the business. You are a party to this transaction as an individual and you need your own legal representation. You will have to be comfortable the price is right, what your shareholding will be and you have to know what the "rules" are . usually found in the Share Purchase Agreement. Your shares may have voting rights, but if you only have 10%, and your colleague has 90%, you're not in a powerful position.
When you say director in name only, the question is:Are you named at Companies House. If so, then it's in more than name.