Dozens of radio stations across the UK are to lose almost all of their local programming in a move likely to result in hundreds of job losses, the closure of dedicated radio studios and regional voices being replaced by programmes hosted from London.

Global Radio has announced that it will replace the 40-plus local breakfast shows across its Capital, Smooth and Heart networks with just three nationwide programmes.

The changes, which will be brought in during the course of this year, are likely to result in presenters and producers across the country finding they are being replaced by big names based far away from the communities they serve.

The number of regional drivetime shows on Capital, Smooth and Heart will also be substantially reduced and all locally produced evening and weekend programmes will be axed. Local journalists, engineers and marketing staff are expected to be affected by job cuts.

Global will close 10 of its 24 dedicated radio studios – in Brighton, Cambridge, Chelmsford, Exeter, Gloucester, Kendal, Kent, Lancaster, Norwich and Swindon – in a blow to the media industry outside the capital.

The shadow culture secretary, Tom Watson, said the job losses were a “travesty” and “particularly damaging at a time when local news is already under extreme pressure”.

“Replacing local voices with London-based presenters will be a terrible loss to communities across the country. Radio has unique reach, providing listeners with national and a local news and friendly company. This announcement is a terrible blow,” he said.

The move will effectively create three new national radio stations, albeit ones that have to opt-out to regional presenters for three hours a day in order to meet the conditions of their local broadcasting licences.

Even those presenters who remain to provide the token regional drivetime programmes on Capital, Smooth, and Heart will serve larger geographical regions than before, covering large swaths of the UK with a single programme.

The move is the culmination of a decade-long project by Global Radio, which has bought up local radio stations across the UK and slowly combined them under a handful of national brands, increasingly sharing programmes across all stations.

For instance, the likes of Manchester’s Galaxy, Cardiff’s Red Dragon and Nottingham’s Trent FM have been combined under the Capital brand, losing much of their regionally produced programming in the process. The change is even starker at the Heart network, which was created in 2008 by rebranding more than 30 distinct local radio stations, all of which will now have the same centrally produced morning programme.

A spokesperson for Global would not confirm the total number of job losses as a result of the announcement, which was first reported by RadioToday, as it said it was consulting with staff. However, the decision to axe about 60 regional breakfast and drivetime shows is likely to leave a substantial number of presenters and broadcasters out of work and reduce the opportunities for new talent to break into the sector.

The Global chief executive and founder, Ashley Tabor, said the decision would result in “significant changes at an operational level” and would allow his stations to compete more effectively with the BBC.

The changes are possible because of new regulations issued last year by Ofcom allowing station owners to reduce the minimum amount of local programming on local radio stations during daytime hours from seven hours a day to just three.

Ofcom also removed a requirement on local stations to produce their own breakfast show, the most important programme on any station’s lineup and one that shapes its identity.

In return, stations have to produce an “enhanced local news service”, which Ofcom defines as meaning the inclusion of hourly news bulletins throughout the day featuring at least one “fully formed local news story” relevant to local listeners.

However, this news output may be produced by journalists based hundreds of miles from listeners. Global’s changes mean one team of news staff will be covering an area stretching from Cornwall to Gloucester.

Global argues that the old system of local radio regulation was designed in a pre-internet era and is no longer appropriate when it is competing with other services for attention.

Commercial radio in the UK is booming, with investment flooding into the sector as the public switch to digital radio and to devices such as Amazon’s Alexa, prompting them to try new stations. However, the focus has been on national rather than local stations.