The two companies have argued that they individually lack the financial firepower to upgrade their 5G networks and have pledged to invest £11bn as a combined company.

Delays to the SRN have sparked scrutiny over the operators’ ability to meet investment pledges.

During a Business and Trade Committee hearing with Vodafone and Three bosses last week, Tory MP Mark Pawsey said: “You’re making promises to us about the investment that will take place if this merger goes ahead. How do we know that you’re going to deliver that if you haven’t yet completed the commitment that you made on the Shared Rural Network?”

Vodafone and Three denied they had neglected the SRN and insisted the merger had no impact on their day-to-day operations.

Phase one of the project is focused on “partial not spot” areas where at least one operator provides coverage but not all of them. Phase two, which will be funded by the Government, targets “total not spot” areas, where no operators currently provide 4G services.

The deadline for phase two is early 2027, though it is expected coverage will be delivered to 95pc of the UK by the end of 2025.

The National Audit Office, which monitors public spending, is currently carrying out a review of the SRN and is expected to publish its findings early next year.

A Three spokesman said: “We are on track to deliver the overall January 2027 target for 4G geographic coverage under the SRN programme having already built 100 sites and secured planning on 80pc of the new sites that we have committed to.

“However, we have recently written to the government asking for an extension to the June 2024 interim target which was agreed immediately prior to the Covid lockdowns and has been impacted by delays associated with the pandemic.”

A Vodafone spokesman said: “We remain committed to delivering on all elements of the SRN programme and have successfully introduced 4G to rural locations across the UK as part of the wider project which is due for delivery by January 2027.”

A spokesman for Virgin Media O2 said: “We’re continuing to invest and deliver these upgrades at pace and we expect to either meet or come very close to meeting our own individual target. We are in regular discussions with government and industry, and remain committed to delivering the full benefits of the SRN as soon as possible.”

A government spokesman said: “All four Mobile Network Operators have been set clear coverage targets as part of their licence obligations, which they are on track to meet and are managed by Ofcom.

“We are in regular communication with them regarding their progress, which the regulator will assess in 2024.”