The race was paused for almost an hour with 190km to go when protestors from the environmental group 'This is Rigged' glued themselves to the road. Police spread powder on the road surface.

The group claimed in a statement posted on social media it had targeted the race due to sponsoring by Ineos, who produce diesel and petrol in Scotland.

As the riders have no earpiece at the event, stewards had to halt the charging peloton on a narrow country lane near the Carron Valley Reservoir, 50km outside Glasgow.

David Lappartient, president of world cycling governing body UCI, was at the scene trying to calm the increasingly restless riders.

The UCI said in a statement it was "working closely with all relevant authorities to minimise disruption to the race and also to ensure the safety of riders as our paramount concern".

Once the race restarted after a 55-minute delay the peloton had nearly 200km to roll to the finish line including 10 laps of a 14km circuit in downtown Glasgow.

The demonstrators first stopped the breakaway group which had opened up an advance of more than six minutes, then the peloton in turn were forced to dismount.

Race favourites including defending champion Remco Evenepoel, Tadej Pogacar, Wout Van Aert, Mathieu van der Poel and Julian Alaphilippe were reduced to waiting, chatting with each other and even posing for selfies.

Sporting events are regularly targeted by environmental activists to highlight the climate and ecological crisis.

Cycle races are particularly vulnerable, being in open, easily accessible terrain over hundreds of kilometres.

Last year, the Tour de France was notably targeted three times.

"This is Rigged" protestors have in the past thrown red paint on the Scottish Parliament building, and blocked refineries last month.