Illiquid?
According to the AIM charts Mentum had over 200 trades in February for nearly 500,000 pounds worth, and over 400 trades in January for over 900,000 pounds worth. That's a lot more liquid than many ASX junior resources stocks.
http://www.londonstockexchange.com/exchange/prices-and-markets/stocks/exchange-insight/trade-data.html?fourWayKey=KYG174761059GBGBXAIM