A union boss has raised concerns that BT’s slashing of 13,000 jobs could impact the telecoms giant’s ability to innovate in the technological space.

BT will shed the roles - 12 per cent of its global workforce - over the next three years and move out of its central London headquarters. Two-thirds of them are based in the UK.

“Many of the roles that BT is proposing to cut are highly skilled professionals and the loss of that expertise could impact BT’s research and innovation capability,” warned Prospect national secretary Philippa Childs.

“We are also concerned that cutting such a large number of roles will inevitably impact those who remain in BT and could lead to work being pushed down to employees in lower grades.

"A well-resourced, highly skilled and professional work force will put BT in a better position to keep delivering world-class results which will help their financial results in the long run.

“The scale of these job cuts is higher than had previously been speculated on and will come as a devastating blow to managers and professionals represented by Prospect.

“Prospect will be calling on BT to take a long-term view about these changes.”

Chief executive Gavin Patterson said BT is looking to cut back its management positions and “consolidate in key towns” to reduce costs by £1.5 billion.

He said around 80 per cent of its staff were based in around 50 offices across the UK and that this will be cut to 30 “modern, strategic sites to create a more collaborative, open and customer-focused working culture”.

BT has been based in St Paul’s since 1874.

“We will certainly have a headquarters in London; this is not BT moving out of London. It is more likely to be in a smaller, future-oriented working environment,” said Patterson.

Shares in BT fell nearly eight per cent in early trading despite it also announcing pre-tax profits rose of £2.6 billion in the year to March, a rise of 11 per cent.

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The firm will hire about 6,000 employees to "support network deployment and customer service". Its standalone subsidiary Openreach, which builds and manages most of the UK’s broadband infrastructure, has already announced 3,500 of these.

BT’s statement said it must respond to “increasing competitive intensity from established companies and new entrants".

It continued: "It is critical that BT transforms its operating model to build a lean and agile organisation that delivers sustained improvement in customer experience and productivity.”

BT currently employs 80,000 in the UK and 18,000 abroad.

“This is probably the most significant transformation we have made in the last ten years,” said Patterson.

“We need to do this to be competitive in the future. If we are compared with our peers we are frankly too complex and overweight.

“While I recognise the pain, ultimately it is the right thing to do for the business.”

The firm also announced a 13-year plan to reduce its £11.3bn pension fund deficit.