The research, by property services giant CBRE, found office rental values in the "donut" around the M25/outer London rose one per cent last month, the fastest rate since July 2000, when it hit 1.4 per cent. That means office rents in the area have risen 4.2 per cent since January.
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To be fair, central London rents also rose one per cent in September - but that was the fourth time since January they've risen by that amount.
CBRE said the strength of the capital has pushed up the average, with office rents for the whole of the UK growing at 7.4 per cent in September, their fastest rate since March 2008.
"The donut has been long talked about as a huge growth opportunity and this data proves the value there is to be found in this region," said Emma Jackson, associate director at CBRE.
“Performance in Central London has remained strong, but the outer London area has caught up in terms of rental growth, driven by a lack of available office space. As occupiers look further afield than Zone 1, the immediate beneficiary has been Greater London, and it’s a trend we expect to continue as supply continues to be constrained in central locations.”