many thanks for all advice - I'm now leaning towards the Svalbard 1 PU - however would like to know more about the advantages besides weight of the SI version. I'm attracted to the Svalbard because it seems (a) quick to put up and (b) robust enough if these pesky gales keep coming. Re mesh inner - is this just the door part?
I looked up the Hilleberg Unna - had to lie down for a while after seeing the price!
In general - PU tents are cheaper to produce than Sil because you're bonding a waterproof layer to the fabric, which is easy and cheap to do in bulk. However Sil tents last longer and it would likely see you 10 years with little to no degradation. In contrast, PU tents get a bit of a 'funk' if stored with a bit of moisture and I'd tend to move a tent on every few years before I have to deal with it becoming worthless or failing totally. Sil also reinforces the tear strength of the fabric which makes it better handle the wind. Biggest killer of tents is always UV though, so don't leave it out on a sunny day!
Essentially dual-sil (manually applied on each side of the fabric) is the ideal for a tent used in wet and windy conditions and what you'd look to find in quality tents, and if you're buying a decent brand (which Nordisk is) then I'd spring the extra 30-40 quid and get the Svalbard Sil for 3.5 season conditions in the UK.
As to the mesh question, you're right, ideally it'd be a solid fabric inner with a mesh door but appears the fabric is mostly mesh - they probably went this way due to how low the flysheet drops to the ground with the intent of reducing condensation, but be aware if you're out in a gale this may want testing and you may find yourself wanting something like a SOL Bivvy to put your sleeping bag in (as it'll cut the heat loss to the environment).