Gemini Restricted Service Notification - October Clock Change 2025 - Sunday 26th October

On Sunday, 26th October the clocks go back one hour at 02:00, marking the end of British Summer Time (BST) and the return to Greenwich Mean Time (GMT). The clock change causes the 01:00 to 02:00 hour to occur twice—once in BST and once in GMT. This “repeated hour” introduces scheduling and data processing complexities. To minimise the risk to customers from the clock change, several Gemini processes are being modified during the 01:00 – 02:00 GMT hour bar.

Please note that both APIs and user interface screens will be impacted during this period.  

The following processes will be restricted with further details provided below and within the supporting information pack: 

• Within Day Auctions (Entry & Exit)
• GB Renominations
• EU Nominations
• OCM & OTC Trades
• Linepack 

Within Day Auctions (Entry & Exit) 

Between 01:00 and 02:00 GMT, Gemini will not allow the placement of within-day bids.  

If you attempt to place bids in entry auctions during this time, the system will display an alert message. Bidding in exit auctions will also be unavailable during this period. The final time to submit within-day bids will be 01:59 BST Any bids placed prior to this will be processed at 02:15/02:30 GMT. 

GB Renominations 

Between 01:00 and 02:00 GMT, the Gemini system will not allow placement of renominations. If you attempt to place a renomination during this period, the system will display the message: ‘Gas Day has expired’. From 02:00 to 02:59 GMT, the window will be open as usual for any required renominations. Any re-nominations placed between 01:00 BST and 01:59 BST won’t be processed until 02:25 GMT.  

EU Nominations 

Between 01:00 and 02:00 GMT, the Gemini system will not allow placement of EU nominations, for Gas Day 25th October 2025. If you attempt to place EU nominations during this time, you will receive an error message to state that “Gas Day(s) range not within Nomination and/or Renomination Acceptance Period”. The last opportunity to place EU nominations for Gas Day 25th October 2025 will be 01:59 BST and these will be processed at 02:03 GMT.  

OTC Trades 

Between 01:00 and 02:00 GMT, the Gemini system will not allow placement of OTC Trades, for Gas Day 25th October 2025. If you attempt to place OTC trades during this time, you will receive an error message to state that “Gas Day has expired”. From 02:00 to 02:59 GMT, the window will be open as usual for any required updates. Any trades placed before 01:55 BST in this hour bar will be approved at 01:55 BST, whilst any placed after 01:55 BST, but before 01:59 BST will be approved at 02:55 GMT.  

OCM Trades 

Between 01:00 and 02:00 GMT, the Gemini system will not allow placement of OCM Trades for Gas Day 25th October 2025. If you attempt to place OCM trades during this time, you will receive an error message to state that “All OCM trades are rejected”. ICE have confirmed that the ICE Endex will be closed from 01:50 BST for the Gas Day 25-Oct-2025. 

Linepack 

Please note that a Gemini Linepack file will be displayed for each hour bar within the 25th October 2025 Gas Day, including the repeated hour 01:00-02:00 GMT. The Gemini system will display all values across the day. We will ensure that the order of files received is reflected in the system.  

Gemini Sustain Clock Change 2025 Supporting Information