The liquidator's job is to obtain the best price for the assets.  If a director wants to buy assets, the liquidator has these items independently valued.  As long as the sale is at the same price or higher than would be achieved on the open market, there is usually no reason why it should not take place.  Such sales often in fact realise more for creditors, as there are no auction or other selling fees involved.

See also below regarding the 'Phoenix company' rules where directors buy the whole business back.