More than 200,000 internet users in Norfolk and Suffolk could see an “astronomical” surge in broadband speeds next year as super-fast telecoms investment gathers pace.

BT’s local network business Openreach has announced that nine exchanges in Norfolk and 12 in Suffolk, including Thetford and Mildenhall, will be upgraded to next-generation fibre technology as part of its �2.5bn nationwide improvement programme.

It will boost connectivity for up to 85,000 homes and businesses in Norfolk and 134,000 in Suffolk – with some expected to achieve download speeds of up to 100Mb/s by the time engineers complete the work next autumn.

Ann Steward, cabinet member for economic development at Norfolk County Council, said: “This is exciting news for Norfolk and fantastic that our work to raise the profile of our county nationally is paying off.

“It is particularly pleasing that some exchanges in the Great Yarmouth area will be upgraded, coming so soon after the news that the town, together with Lowestoft, is to become an enterprise zone.

“This is the kind of shot in the arm this area needs – and will make the town an even more attractive location for companies.”

Openreach aims to supply fibre broadband to the most economically-viable two-thirds of the UK by the end of 2015. The largely remote and rural “final third” is expected to be reached by local authorities with the help of government funding.

Six of Norfolk’s 142 exchanges had previously been announced on BT’s upgrade schedule. When the current round of work is complete, the total number of customers able to access the county’s new network is estimated at 131,000.

Dave Hughes, BT’s regional director for the East of England, said: “Our latest investment will propel internet users at home and at work into the 21st-century fast lane.”