How much money do you want to spend?
Your dad needs a road bike. He can keep his mountain bike for playing at the weekends. However, for the sort of work that your dad needs, he doesn't need suspension, fat tyres, XC gearing or even geometry.
The hybrid is not a bad sugestion, although I would look at something with road wheels and tyres.
I ride a mountain bike and have started riding against cyclo cross machines. Although my 26" wheels will out accelerate them in a short burst, once those larger wheels get going I get twonked.
The same aplies with a road bike. This has not been designed to snake through twisty bits and take out rocks and routes. It is designed to eat up road miles efficiently and quickly.
For about £100 - £200 you will be able to get a Raleigh, Apollo or Falcon. These are OK. You are probably looking at at a steel frame, with basic components. This will probably do him.
Spend a bit more money and your optins become more viable
For about £200 - £300 and you can expect an allumium frame, with viable components, like Dura Ace cassets, decent saddles, nicer hubs etc. All of which will be lighter than their cheeper alternatives. They will also be more consistant and probably last longer. I would look at Claude Butler, Dawes, Trek, Giant.
Start spending more money and you will have, not just a nice bike, but a really nice bike. Frames will boast processes like Hydroforming, or heat treating. Handle bars and finishing kit will be nicer. Gears will definately get nicer, with things like trigger shifters on the handle bars etc.
However, for what your dad needs, this last category is a bit of overkill. Keep it simple, keep it light. You might consider paniers or some sort of luggage carrying for the back. This will be usefull for stowing the packed lunch and a change of clothes. He would also benefit from mudguards and decent kit, like a multitool, pump and especially lights (This last one, along with a lid, will definately save his life on dark winter nights.
Go to these web sites and have a look, especially at the second group of bikes:
www.evanscycles.co.uk
www.paulscycles.co.uk
www.rutlandcycling.co.uk
www.pitsfordcycles.co.uk
www.georgehallcycles.co.uk
Luck