This is the sequence of shots showing both males mating in succession with the female.
The male behind the female is mating, the one on top beats its wings
The first male is dislodged
The second male mating (also in the top shot)I have been unable to find - or access - published research about Merodon mating behaviour or how frequent this multiple mating is. It is also possible that I missed a struggle between the males and the second managed to dislodge the first one. After mating, the female will look for daffodil or bluebell bulbs to oviposit. The larvae will feed on the bulbs and these will die or bear no flowers next spring.