We have two Decathlon blackout tents and it's very effective, also helps to keep the sleeping area cool although maybe that's more to do with the tents being white.
Thanks for the advice, everyone.
Just ordered a Coleman Spruce Falls 4 Blackout since I found it on offer (or at least, I found a shop that was selling it cheaper than in the other shops) so we'll see how it goes.
@stevenmenmuir how is the white holding up. We came close to buying the decathlon black out but couldn't get past the fact it's white.
I think a bug proof living space is pretty much an essential for us as my experience of Scotland as a kid is that any gap no matter how small will let the midges poor in. I've had them come through the air vents in cars before.
The little buggers (I mean the midges, not the kids) will always find a way in, but definitely better having the fully sealed inside. We've survived windless days in ours in Skye and the west of Scotland in summer.
Ally. If you do, buy the 2 pack of king poles, much better than the one it came with . If it's windy I drop one side, if the wind changes while we're out, I drop the front right down. Like I said I made a wee sling that the guylines are secured to so I don't wear out the webbing eyelets which I think is a design error on vangos part.
Thanks @jamiemcf. Ordered the Vango last night. I'll get more king poles if I don't already have some suitable - think I do, but can't remember where... And thanks for the tip re the attachments, I'll be sure to modify in advance - I think I understand what you mean in your earlier post!
The decathlon air beam tents are really good. the outer fabric is an off white which has held up really well on ours. It's also quite thick/heavy weight nylon compared to many tents and is really well made.
The material on the black out inners is noticeably thicker and more black-outy than e.g. a Berghaus air tent we looked at. they felt a bit see through and thin compared to the decathlon ones.
black out inner are a revelation for kids (and adults...) sleeping.
The Decathlon blackout tents are so effective its difficult to find stuff in daylight hours. The flysheet in the sleeping areas is foil backed so helps to keep it cool and does most of the black-outing, and also has black inner tents. I think alot of other 'blackout' tnest simply have black liners.
That's the bumper load of cams I found either at decathlon at £40 a pop or the last load of friends at knock down prices before their redesign.
Ally best crop I could get of the pear million on the front central one. 
