sorry - thought I understood it all, but I don't! sorry did some more looking around on the internet into what type of bike would best suit me, taking onboard your advice from what I can see we're saying:

MTB with slicks - fine to start, but will add 20-30 mins to the trip, not ideal. Will start with this, cause I have one and see how I get on. I'm also ruling out a true road-race bike due to the lack of comfort, and "twitchyness" which might not lend itself to my commute.

This sort of leaves me with 3 options -
1) Hybrid / Road Cruiser - I fully get that the straight bar will be less comfortable / dynamic than other options, but on the plus side they tend to cost a lot less. Also I'm more used to cycling straight bars, but sure I could adapt as needed. I think these give you a lot of the benefits of a more traditional road bike, with straight handle-bars, would this sound about right?

2) Cyclocross - from what I can see are like racers that can take wider tyres, and have a more stable frame. These look to be ideal for what I'm considering BUT they seem very pricey. The cheapest I can find, start at about £500, so this might be out of my budget, unless I buy 2nd hand. If I do, then I can't get the 40% off option.

3) Touring bike - are more durable / stable versions of race bikes. They are built to take more weight / gear on them. They seem to cost about £400 + too, slightly less than cyclocross, but still up there. Might be at top end of my budget too.

Suppose what I'm trying to get my head around is if these are my criteria, which is the best bike for me:
- Max spend £300
- always used on roads only
- won't be carrying much gear with me
- needs to be comfortable enough, spending 2-2.5 hours on it
- needs to be sturdy enough, dont want to get knocked off too easy

Would a hybrid / city bike like in point 1 maybe do me, or would the benefits of having a traditional handlebar be that big. Sorry if this is a stupid question!