Hi Kev,
Based on average PA-28 speeds, factoring in wind etc, to fly *direct* from Bournemouth to Manchester would take something between 1 hr 15 and 1 hr 45 min...very roughly. You wouldn't normally need to stop and refuel for a flight of that length.
A direct route doesn't however take into account such factors as weather, controlled airspace etc. The direct flight time wouldn't be affected so much by the latter (given good planning) but the weather will affect your dispatch rate (ie. the number of times you can safely make the trip) dramatically. Unless you have an instrument rating and a suitably equipped aircraft (this costs a lot!) you will probably have to cancel anywhere between 40%-30% of the time, at best, depending on season.
Have a play around with the route function on this.
SkyDemon Light You can plug in various winds and speeds in the lower right corner. For a PA-28, use 100 kias, and windspeeds between 10 and 30 knts to get a rough ballpark. (You may need to download Silverlight, but it's free).