Price spike
Research notes
Figures are for London unless they say otherwise.
What happened
- London max 55.3p at 18:30, avg 22.8p, and the day's minimum was as high as 13.5p. Highest anywhere 63.9p in Northern Scotland. The only day of the summer to meet the high-price threshold. July's London monthly average was 18.2p.
Likely causes
- It was the hottest day of 2025. The Met Office first reported 34.7°C at St James's Park, then after verification 35.8°C at Faversham, Kent. (confirmed by source) Met Office on X, 1 Jul 2025, Met Office on X, verified figure
- Wind was low: 3.8GW average against a summer average of 6.0GW, and only about 2.5GW at midday and 4GW in the evening. (confirmed by source) Elexon FUELHH 1 Jul
- Gas did the work. Gas-fired output averaged 12.2GW, the second highest of the summer (only 13 Aug was higher, at 12.3GW), never fell below 9.7GW even at midday, and ran at 13.8 to 15.1GW from 16:00 to 20:30. (confirmed by source) Elexon FUELHH 1 Jul
- Demand on the transmission system was the highest of the summer: INDO averaged 25.9GW against a summer average of 22.1GW, peaking at 29.2GW at 17:30 to 18:00. Solar was modest for a hot day, peaking at about 8.6GW (the record a week later was 14.0GW), which pushes transmission demand up. (confirmed by source) INDO 1 Jul, PV_Live 1 Jul
- The continent was far more expensive than Britain that evening. Ember: "During peak evening hours on July 1, prices reached over 400 €/MWh in Germany and over 470 €/MWh in Poland". GEM Energy Analytics gives the day-ahead price for the 20:00 CET hour (19:00 UK time) as €517.57/MWh in Belgium and the Netherlands and €476.19/MWh in Germany and Denmark. Ember puts the cause down to heat-driven demand (up as much as 14% in Spain, 9% in France, 6% in Germany), low wind, and French nuclear cuts, with at least 7GW of French capacity marked as forced outage on 1 to 2 Jul. (confirmed by source) Ember, 4 Jul 2025, GEM Energy Analytics, 3 Jul 2025
- The interconnectors show the continent pulling on Britain. At midday Britain was importing about 6.6GW. By the evening net imports had fallen to 1.2 to 1.9GW, and Britain was exporting at or near full capacity to the Netherlands (BritNed, about 1.0GW), Belgium (Nemo, about 1.0GW) and Denmark (Viking, about 1.1GW) from 19:00, while still importing from France and Norway. At 18:30, the half-hour of the price peak, exports were 0.7GW to the Netherlands, 0.25GW to Belgium and 1.1GW to Denmark. (confirmed by source) Elexon FUELHH 1 Jul
- NESO's commentary for the day: "Trades were required for Margin", meaning the operator bought extra power to keep enough spare capacity. The day before it had described the system as "very constrained". (confirmed by source) NESO daily balancing costs, Jul 2025
- My reading: a hot, still day meant Britain needed a lot of gas generation at home, and the evening peak was then priced up further because neighbouring markets at €400 to €500/MWh were bidding for the same power through the interconnectors. The GB peak was far lower than the continental one, which fits Britain being better supplied but not insulated. (inference)
Wider context that week
- The new Ofgem price cap took effect on 1 Jul: down 7% to £1,720 a year for a typical dual-fuel direct debit household. A useful contrast for a post, since the cap fell on the same day Agile had its most expensive evening of the summer. Ofgem
- The IFA1 cable to France returned to its full 2GW on 1 Jul according to Montel, and the Elexon data shows about 2.0GW flowing from France at midday. Montel also notes that from early July France "consistently exported more than 10 GW per hour". Montel commentary, 3 Sep 2025
- June 2025 had been the biggest month for solar in EU history (45TWh), which Ember credits with keeping daytime prices down during the heatwave even as evenings spiked. Ember, 4 Jul 2025
- Montel's Q3 summary says of the whole quarter that "cooling needs during heatwaves drove short-lived spikes in consumption and prices". Montel Q3 2025 summary
- On 10 Jul the government published its decision to keep a single national wholesale price and reject zonal pricing. Norton Rose Fulbright on the REMA summer update, the government document
Confidence
High on the ingredients (record heat, low wind, very high gas burn, highest demand of the summer, extreme continental prices, evening exports), all of which are in primary data or named reports. Medium on how much each one contributed, because I found no GB-specific market report for the day.
Gaps
- No Bloomberg, Reuters, Montel or trade-press article about the GB day-ahead price for 1 Jul 2025, and no £/MWh auction figure. The continental coverage does not mention Britain.
- Be careful with a very similar event a year later: an Inspired PLC article and Reuters and Bloomberg reports about a £157/MWh GB price during a heatwave are from 23 to 25 Jun 2026.
- I did not find anything on specific GB gas plant or nuclear outages on the day. Nuclear output was normal for the summer at about 4.6GW.