@Jura and I got into this a week or two ago.Pressure mounts on UK defense chief over pick of Boeing surveillance plane
The British MOD seem Skittish about the A330-Erieye. There is a history here for why though. Before the British bought Boeing's E3 they had tried to go the indigenous route.
British history of AEW though is... Well when they get it right it's good when they get it wrong.... oh boy.
The last attempt was the British Areospace Nimrod AEW3.
As the name implies it was based on the old Hawker Stanley Nimrod MPA. But the issues of the program caused it's its cost to balloon the system was plagued with issues it's first flight was 82, introduced in service 84 retired 86.
Before that the "Stop gap" Shakelton AEW2 based on a retrofit of a post world war 2 design derived from a world war 2 bomber. Introduced in service as an AEW in the 1970s. Fitted with a radar taken from the "Stop gap " Fairey Gannet AEW.3 it's predecessor which intern took that radar from the Douglas AD-4W Skyraider a world war 2 vintage American aircraft.
So yes the British MOD are being conservative. Because a consistent theme of there AEW is being offered a new design down the line only to have it cut and interim stop gaps remaining in long after they were supposed to be replaced. The A330 Erieye combination has never been built. It's easier for the Parliament to cut a paper airplane then a existing product. The MOD feels the need to get a AEW right now, and they don't want approval today cancelled tomorrow because the integrator is suddenly upping the price estimate.