* System oversupplied by nearly 30 mcm
* Norway focuses gas exports on Britain
* Day-ahead contract rallies
Sept 2 (Reuters) - The British spot gas price dropped by 15 percent on Friday, touching a fresh seven-year low, extending losses this week, as the system struggled to cope with a massive supply glut.
In volatile trading, gas for immediate delivery hit an intra-day low of 19.85 pence per therm mid-morning, before recovering to 22.50 p/therm.
Several factors, including the inability to clear away surplus gas into storage sites fast enough and Norway focusing its exports to Britain, contributed to a 30 percent fall in the within-day price this week.
Britain's gas market was oversupplied by 28.9 million cubic metres (mcm) on Friday after a sharp jump in Norwegian deliveries, driven by the producer's inability to send gas to the Continent due to technical issues.
As Norway diverted gas deliveries to the UK, the day-ahead gas price at the Dutch TTF gas trading hub rallied sharply, up 3.50 percent at 12.30 euros per megawatt hour (MWh).
On the British gas hub, the day-ahead gas price surged 14 percent to 24.40 pence per therm, due to expectations of less supply being available from Norway going forward.
Exports from Britain to Belgium were nominated at near full capacity of 56 mcm/day as relatively cheap UK gas drove purchases by continental end-users, analysts at Thomson Reuters (Dusseldorf: TOC.DU - news) said.
In the EU's carbon market, benchmark EU allowances fell below 4 euros to an intra-day low of 3.89 euros, their lowest level since March 2014.
The sell-off was triggered by a poor German carbon auction which had a cover rate of just 1.42.
EU allowances recovered slightly to 4.13 euros a tonne by 1047 GMT.
(Reporting by Oleg Vukmanovic and Nina Chestney)