Lorries being driven in London could be required to fit an “extra window” to their passenger-side doors, under plans unveiled by Boris Johnson to tackle deadly blind spots.

The Mayor today launched a consultation on requiring the lower panel of the doors to be replaced with a glass panel, effectively creating a a transparent door, at a cost of £1,000 to £1,500 per HGV.

Firms refusing to comply could face fines of up to £1,000 and the threat of losing their operators’ licence.

The extension of the Safer Lorry Scheme comes after seven of the nine cyclists killed in the capital last year involved lorry collisions. Since last September, vehicles over 3.5 tonnes are required to fit extra mirrors and side guards to prevent cyclists or pedestrians being dragged under their wheels when the vehicles are turning.

Transport for London today announced the first successful prosecution of two firms to breach the rules, which apply on all roads excluding motorways within the M25.

The latest proposals would be enforced by the Met police, DVSA and TfL’s HGV task force under an extension of the congestion charge or lower emission zone rules. The “in principle” consultation closes in March, meaning it would be for the next Mayor to decide whether to impose the new sanctions after finalising the details. New restrictions could apply 24/7, at peak hours or only on certain routes.

Mr Johnson said: “The danger caused by HGVs to other road users is unacceptable and we have to reduce it. With the launch last year of my Safer Lorry Scheme, we have already made real progress.

“Seven of those nine cyclist deaths involved lorries and that is why we have to press on to the next stage. The cost per lorry is modest. The benefit to Londoners’ safety will be significant.”

Two haulage firms, D & R Grab Hire Limited and What a Load of Rubbish Limited, were each fined £500 plus £235 costs by City of London magistrates last month for having no Class VI mirrors or side guards on one of their vehicles.

TfL said that since the Safer Lorry Scheme launched last September, 5,610 vehicles had been targeted and stopped, with 269 of those found to have been in breach of the new rules.