A tricky question which needs quite some thought
Here are my top places of interest
Cromwell's troops when quartered in Reading, made reference to a locally bred pig renowned for its size and the quality of its bacon and ham. This turned out to be one of the earliest records of the Berkshire breed
The British Saddleback is the result of the amalgamation of two similar breeds, the Essex and Wessex Saddleback
The Hampshire is one of the World’s most important breeds.
The Large White owes its origins to the old Yorkshire breed.
The Large Black, one variety is to be found in East Anglia and the other in Devon and Cornwall.
Then there is The Oxford Sandy & Black Pig
The Tamworth, the oldest pure English breed
There's the Welsh pig which comes from the 1870’s when there was a considerable trade in Welsh and Shropshire pigs into Cheshire
and finally who can forget
The Gloucestershire Old Spot famed for grazing in the apple orchards, and clearing up the windfalls. They predominantly live outside throughout the year and are therefore known for being tough and hardy, although also quiet and easily handled.