TBH I think I'm swinging more and more towards the Roadrat. I've yet to hear that I can definately get one via my work's particular scheme, hence still wanting to hear about more "mainstream" possibiities should I have to resort to Halfords.
You can order a Roadrat through Halfords no problem – I ordered mine through my works scheme from there the year before last. I went into the store, told them what I wanted and they put it through on special order. I think I just had to call Cotic first to check on stock.
For what it's worth, I'd say it's a good match for what you're looking for and ticks all the boxes. You will probably need to be careful with tyre choice though given your mixed commute. I run drops and cross tyres on mine and it will go in most stuff, althought it gets a bit sketchy on really rocky trails. Absolutely rips on tarmac, fire roads and smooth singletrack and is a great mud bike.