If you look at the interims a few months ago they said
"Sales of alkaline phosphatase have increased by 78% which includes the fulfilment of part of a large order from a major customer who generally orders once every 18 months.
....I suppose if this was in H1 last year, "18m later" may get in before the end of H2 this year and so my statement that it wouldn't happen this year would be incorrect. However if it happens right at the end of H2 this year, re-ordering 18m after that would definitely mean a year without the order.
In summary the point is that the past year is flattered by a large order which is made less than annually.
I believe (slight guesswork) the large customer who orders on a non-annual cycle is Diagnostic Products Corporation