The Macmillan Cancer Support Etape Caledonia was sabotaged for a second time when the 2011 edition took place on Sunday – with tacks, drawing pins, screws and staples strewn along the route.

The 81-mile cyclosportive, in Perthshire, Scotland, was first hit by protesters in 2009, when the ride was suspended for 90 minutes and hundreds of riders suffered punctures.

This time out the event was not disrupted, with organisers spotting the debris, between Weem and Strathtay, and clearing the affected area before the 5,000 riders set off

Police are appealling for witnesses to what they say was a “reckless and completely irresponsible” act.

The saboteurs are thought to be angry that the ride, reportedly worth more than £1 million annually to the local economy, takes place on closed roads.

The Anti-Closed Road Events pressure group has condemned the attacked but, in turn, stepped up its own efforts to declare the Etape Caledonia illegal.

“We believe that it is time to launch a serious bid to have this race stopped as we are firmly of the view that it is illegal,” ACRE spokesman Peter Hounam told The Courier.

“ACRE is now planning to liaise with Tayside Police to ask them to take legal action against the organisers of the Etape.

“We have also made efforts to get the Scottish Government involved and believe there are concerns being raised there, too.

“This race as it is now, with its 5000 riders, is not what the legislation they are running the Etape under was designed for.

“When the organisers came along to sell this thing to the community it was of vital importance to them that it be thought of as a trial and not a race. I don’t think there can be any doubt that it is a race.”

Meanwhile, two cyclists were airlifted to hospital after a collision during the event.

The accident happened on the Tummel Bridge with the riders, both from Essex, taken to Ninewells Hospital, one suffering a “significant internal injury”.