I live near Bridport. It’s a mixed bag; there’s a fair amount of good riding, mostly very hilly, with some amazing bridleways and hollow-ways, the Dorset ridgeway to the East, Symondsbury Estate has an 8 mile mountain bike route, The bridleways around Beaminster can be linked up to make some good routes. And the views are always impressive. There are a lot of hereditary estates locally, which often have reasonable bridleways for the hunt. The downside is that there are a lot of localised variations as to how accessible the routes are – there are a lot of gates! There are a couple of MTB groups that meet for rides locally. They might be worth a punt to discover some trails.
To be honest, Suggsey, you’re not missing much on Chesil Beach – it’s a shingle/pebble beach all the way – an absolute nightmare to ride.