Their accounting policy is very conservative, which will mean they will defer showing revenues until they have met strict revenue recognition requirements.
"Turnover
Turnover represents the amounts (excluding value added tax) net of discounts allowed derived from the provision of goods to
third party customers during the year to the extent that all obligations relating to that turnover have been fulfilled in accordance
with FRS 5."
What will ultimately be important to investors though will be the cashflows, rather than the timing of revenue recognition, and they seem to quite healthy over the past two years. Even if the orders are once every 18 months, the timing of meeting the fulfilment criteria for those orders will be variable from year to year so it will be difficult to predict the accounting revenues but even so, I find it re-assuring that at least the company is not counting its chickens before the eggs hatch.