Hi confusedcyclist,
I was going to suggest the Genesis Day One and also the Pinnacle Arkose Alfine but luckily they've already been mentioned above. Whilst the Day One comes with mudguards already fitted (plus I have a personal preference for steel over aluminium) I'd definitely consider the Pinnacle especially considering the brakes. I've not yet tried either of the specific brakes in question but going by spec I'd probably prefer the TRP Hylex Hydraulic disc brakes on the Pinnacle Arkose compared to the cable operated Promax brakes on the Day One. Either way if you can I'd try to get a test ride on these bikes or any others on your shortlist if you can.
In terms of other options I'd take a look at the VSF range because they have several bikes offered with hub gears but apologies as I don't know the current prices. The T500 is now available with disc brakes plus has extra things including the mudguards and hub powered lights which in my eyes is a massive bonus for a commuter.
https://www.fahrradmanufaktur.de/en/
If you're anywhere near Cambridge you could try to pay Chris Bikes a visit to see what you think of the VSF bikes.
http://www.chrisbikes.co.uk/bikes/
As mentioned above there are quite a few internal gear hub bikes offered by Cube.
There's the Cube Travel SL
https://www.cube.eu/en/2018/bikes/trekking/tour/travel/cube-travel-sl-blacknblack-2018/
The price of the 2018 model seems to be around £1,150 and so would be over budget unfortunately. However just as an example a coupe of months ago this place had the 2017 version for £879:-
https://www.freeborn.co.uk/cube-tra...MIxMXykvCq1wIVhpO9Ch06JwvPEAkYBiABEgI0QvD_BwE
There are also other bikes in the same range being the Travel Pro, Travel Exec and just the Travel (all with disc brakes) which might still fit your wish list but be cheaper than the SL version. But one thing about the Cube that bugs me is that for me personally the mudguards are too short.
https://www.cube.eu/uk/2018/bikes/trekking/tour/travel
There's the
Kalkhoff Durban 7
https://www.kalkhoff-bikes.com/en/bikes/2018/bikes/urban/durban-7.html
Ignore the photo of the step through frame on the main picture because it is available as either a step through frame or with a top tube. A while ago it was available here for £529 however it's rim brakes only I'm afraid but this is probably reflected in the price. However maybe Kalkhoff do some disc brake bikes as well but I've not had time to look right through their range.
https://www.edinburghbicycle.com/kalkhoff-durban-7-2018-mens.html
There could also be some bikes in the Bombtrack range that could fit your requirements but again unfortunately I think that they'd come out over budget. But if you like their bikes it's worth looking into because it's not easy to find the UK prices. If you're near one of the shops in the UK that sell them you could ask them about the prices and ask the shop if they'll take the cycle scheme voucher that you have.:-
http://bombtrack.com/touring/arise-tour
http://bombtrack.com/touring/beyond-xpd/
http://bombtrack.com/urban-2/arise-geared/
http://bombtrack.com/outlaw2/
Depending on where you are if you search the find dealer section of their website it says that there are dealers in Lyndhurst, Worcester, Oxford, London, Ipswich, Scarborough and Ambleside.
Good luck finding the right bike for you!
John