Watchdog Ofcom has dropped its probe into whether BT had breached rules meant to protect small firms from large costs, after it reimbursed all affected companies.

The investigation was launched in July last year after allegations that BT overcharged businesses when installing high-speed lines into offices.

Ofcom has now dropped the case on "administrative priority grounds", after Openreach voluntarily reimbursed all affected businesses.

In May 2014, new rules were introduced which meant BT must absorb the first £2,800 of excess construction costs (ECCs) associated with installing technology into businesses signing up to their leased line services.

Last summer, the regulator said it believed BT may not have applied the ECCSs to a number of firms.

But on dropping the case, it said: "Having gathered and reviewed further information from Openreach, we have decided not to proceed with the investigation on administrative priority grounds."

The regulator said the move comes "in light of the limited consumer harm and the proactive steps Openreach has taken to address the issue, including voluntarily reimbursing all affected telecoms providers for the full amount of the ECC overcharge including interest".

Ofcom said it would continue to monitor Openreach's compliance.

The news comes after BT Openreach announced plans to make ultrafast broadband available in more than 200 market towns and villages across the UK, with Saxmundham in Suffolk named as a new location alongside Aberdare in South Wales.

This will build on successful trials from last year, which saw full-fibre network put into areas previously considered too complex or expensive to upgrade.

This is part of BT's aim to reach four million homes and businesses with full-fibre technology by March 2021.