Cheers for the answers so far guys... Food for thought certainly...
A bit more info...
I'm just shy of 3 miles from my nearest train station, there is ZERO parking there so I'd have to walk to it... The trains are only every hour, ridiculously, so though it's a direct route, I'd be leaving home before 7am to catch the 7:45am train that gets to the destination at 8:30am to start work at 9am... The journey by motorbike is under 40 minutes... Even by car, with traffic, it's around an hour, though would then have to find somewhere to park the other end around a mile from work which would mean a 20min walk that end too...
Clothing wise, not a problem... Already own a Rukka suit, suitable boots and gloves, heated clothing etc... The kind of kit I'd have no qualms about setting off for a full day ride in questionable weather, so a 40min commute each way would pose no problems...
I hear where
@Taff is coming from on the middleweight Adv bike... Thing is, I already own a heavyweight Adv bike that does 55mpg ridden sensibly... It would certainly do for the moment at least...
As
@weeksy says, I think the Big Scooters really have merit for commuting... Thing is, decent ones aren't cheap of course! The Honda X-Adv 750 (basically a cool, scooter version of the deeply unfashionable NC750) really looks the part, makes the right noises etc... But you're dropping £10k on one, saving £10 a week on fuel at best (they typically do around 70mpg compared to low-mid 50's compared to what I have already), and that's just for commuting on... Hard to justify, even for the most competent of man mathematicians!
@Noggin makes a good point about a smaller, more involving bike, and I've certainly had the same thought... When the weather's good, it would be ideal, keep your focus up, keep costs down and be pretty good fun in the way that anything with a total lack of power is when you have to wring its neck most of the time... Problem would come in the depths of winter, no fairing, no creature comforts, and just wanting to get home quickly and stress free after a day at work, not wanting the commute to become an event in its own right!
@Count Steer's point about costs isn't as ridiculous as it might sound... Train ticket (which I've kinda ruled out because of the ludicrous 2hr combined time each direction because of the walk involved at my end) is £2600 annually or £250 per month...
@Rockburner's point about a bike that's easy to maintain yourself does have validity, but then if you're riding it 5 days per week for 48 weeks per year, are you going to want to spend the time to work on it yourself too?!?! Then
@v8-powered makes the point about commuting on a bike that you don't really care about... Either way... I keep coming back round to the most unloved of Sports Tourers that there are still plentiful of good ones about for under £2k, superb engine, they have an INCREDIBLE headlight (from Nov-Feb, return home journey's would be made fully in the dark) which is very rare for a motorbike, and they're absolutely bombproof with nothing more than routine maintenance... And I've already owned 2 of them in the past and know a fair bit about them to be fair... The 5th Gen Honda VFR800! The only real downer is they're not particularly great on fuel, high 40's to 50mpg average maybe... But buy a good low miler for £2k now, add 30k miles on it over 2years with nothing other than routine maintenance, and it would still be worth £1200 in 2 years time... Comfortable too, and really only needs heated grips adding to make the commute bearable (I love cruise control on boring roads, but this commute would be on mostly quite open roads where I'd not be using cruise control anyway).
Regardng carrying stuff... Not a lot, only a change of clothes for the day really I guess... Would certainly fit in a typical top box (already have a Givi V47 I could use so would just need a corresponding base plate for any bike).
And yes... I do worry that it would diminish my desire to ride motorbikes for fun in my own time too... But I have other hobbies there too, so as a temporary problem (I don't see me doing this role for more than a couple of years, should I be offered it) I don't see it posing too much of a long term problem for my love of 2 wheels...
As for electric motorbikes... Well I think that small, light ones for urban duties work really well... But the kind of commute I'd be doing, I'd need something capable of much greater speeds and distances, and that costs serious £'s... Which really would be a false economy I suspect. I'd probably rather spend the money on an electric car or van instead to be honest, and then plan to use that more...
Realistically, I understand that I'm likely to want to take the car on occasion, certainly if the weather is bad enough... I need to work out a contingency plan there, where to park, do I keep a mountain bike in the back of the car too to turn the 20min walk into a 5min cycle ride etc... I'm also likely, on a nice day, to want to give my Indian the odd run out too, to make the commute a bit more interesting from time to time...
For what it's worth, I've also applied for a role, with a motorcycle dealership ironically, that I could walk to and from work every single day (or cycle) as it's only just over 2 miles each way...

Applied nearly 2 weeks ago and still heard nothing back mind, so hey ho...