I did finally get an answer from ARCAM confirming the lack og gapless with FLAC files.
"The choice we had was to make the unit universally compatible with UPnP servers and controllers, with wide compatibility for open audio formats, or restrict use to a single app and file format to allow gapless playback. We chose the former, so although it does not support gapless playback it does mean that you can use any UPnP app to control it. This is one reason why there is no Android app in development -- my particular app of choice is Bubble UPnP."
Oh well, although my Yamaha player does do gapless and can be controlled with other apps.
The search continues.
I have a Pioneer N50A, and it does gapless or it doesn't do gapless depending on your point of view and how you use it. If you ask the Pioneer to fetch the data from the DLNA server it will happily play gapless, on the other hand, if you ask the DLNA server to send the files to the Pioneer then it does not play gapless. The Pioneer app is crap, and the front screen is tiny, so it's rather annoying to say the least. I have to wonder why the Arcam wouldn't operate at a minimum like the Pioneer.
The DLNA standard is a mess and gapless depends on the correct prefetch information being sent, I guess with some servers the Pioneer might also have an issue, in which case they may get complaints about it not being gapless. Is this perhaps the reason opted for the easy but utterly shite solution?
BTW, I get round the Pioneer issue by having a playlist that I drop what I want to play into, and selecting it with the Pioneer. Only a couple of more button pushes and it works. In the end it's still a work around.