It's not a Northampton issue, it's a High Street issue. There is barely a vibrant town centre left in the country, even central London is half vacant.
It's all about online and retail parks. The town centre is effectively a white elephant, I can't think of many reasons to go there. The places that do better are usually smaller towns with local independents, although everywhere has obviously suffered the past 12 months.
It was always previously a Northampton issue though. The Council commenced the destruction of Northampton Town Centre (and the rest of the town for that matter) in the late 1960's.