NESO Issued Emergency Interconnector Calls on June 23 as Cross-Border Flows Swung Against the UK
Elexon data show GB drawing over 3.8 GW from three cables at midday on June 23 before cross-border flows swung against Britain within hours.
A retrospective published by Energy Voice on Tuesday (2026-09-22) reveals how close the UK came to a serious supply shortfall in late June, with Ofgem confirming that grid operator NESO issued emergency requests for interconnector assistance to both the Netherlands and France on June 23, 2026.6
At midday on June 23, the UK was drawing on every European neighbour available. Elexon data show Denmark's Viking Link delivering 1,424 MW, Norway's North Sea Link supplying 1,398 MW, and the Netherlands' BritNed adding 1,044 MW, with Belgium's Nemolink and the three French cables — Eleclink, IFA and IFA2 — all exporting to Britain simultaneously.6
Five hours later, the picture had reversed. By 5pm, Viking Link was requiring 1,194 MW from the UK, Nemolink had swung to 736 MW out of Britain, and BritNed was taking 838 MW away from the system. Interconnector economics run on price signals, and when Continental prices shift, the flows follow regardless of where the GB system sits in its evening demand ramp.6
"Normal economic behaviour is in the summer, gas goes off, in the evening they come on again," Glover told Energy Voice. "What materially changed was the interconnectors. It's to do with how fast the interconnectors ramp." NESO, he said, should have issued an electricity margin notice on June 22 but did not. Two EMNs were eventually issued on June 24 and June 26 — the emergency signals to generators to make more capacity available.6
Unplanned outages peaked at 4.3 GW at 16:00 as conditions tightened. Wind had been the largest electricity source across the quarter, but curtailment of more than 2.4 TWh in the final week of June, per Montel data, stripped back generation at precisely the wrong moment.6
NESO has since capped total interconnector trading with France, Denmark, the Netherlands and Belgium at 1,500 MW, with a maximum of 300 MW on any individual cable, through the end of 2026, Montel reported citing NESO. That ceiling sits well below the midday June 23 import volumes from Denmark and the Netherlands alone, which together exceeded 2,400 MW.3,6
Montel reported in July 2026 that four UK power interconnectors faced "exceptional" restrictions on electricity exports on July 17, 2026, with the operator warning that constraints could have a material impact on power prices if they persisted.4
The June episode sits awkwardly against the UK's stated interconnector strategy. Britain now operates eight interconnectors with total capacity approaching 10 GW — roughly a fifth of peak consumption — and regulators want to nearly double that to 18 GW by 2032, The Economist noted. National Grid estimated in 2021 that current and planned links would save consumers £20bn by 2045. Expanding capacity is a different calculation when the operator is simultaneously capping what already exists.1
NESO's Summer Outlook had anticipated Great Britain as a net importer under both high and low gas price scenarios, with Viking Link rated at 1.4 GW of import capacity. June 23 showed how quickly that assumption can unravel.2
Norway NO2 day-ahead power sat at €125.07/MWh and Denmark DK1 at €154.29/MWh on Tuesday (2026-09-22), spreads that in ordinary circumstances would drive substantial flows toward the UK. Under the 1,500 MW import ceiling, much of that potential is blocked. NESO's Winter Outlook, published September 1, 2026, sets the planning baseline for the season — but it is the June afternoon, when the cables turned at the worst possible moment, that traders will keep coming back to.5,3