Thanks both for your replies.
My commute can either be 100% on road, mostly flattish with a few steep hills no more than 200metres long, or I can spend about 15 miles or so on the network of canals between Langley Mill and Sawley (for those of you who know the area).
I start work at 5 am, so both options will be very quiet. The return journey starting at 4.30pm is a different matter though!
I am (a young) 48 years old, so no longer worried too much about fashion or breaking any records, but do want to get home at a reasonable time!
My large family means I am on a tight budget, and can only afford one bike, which I need to be solid and reliable, so while I would dearly love a drop bar sports bike, I would worry about it being a bit fragile.
Thanks again for the advice, it is very much appreciated.
Edited to say - Riverside 5 forks deffo have no lock out - Riverside 6 does but its another £250! ( and Im not bothered about disk brakes anyway.)