Royal Mail has detected a rise in Dark Web dealers sending drugs through one of its sorting offices, police have revealed.A number of Christmas and greetings cards containing cannabis have been intercepted in recent days at Royal Mail’s office in Swindon, addressed to destinations nationwidePolice were alerted by staff who could smell the Class-B drug through the envelope.Inspector David Tippets, from South Swindon Police, said the force had identified around 30 similar packages in Swindon over the last six months.”It’s normally cannabis, because it’s got such a strong smell, if it’s in an envelope and there’s an obvious lump it gets easily identified,” he said.”Some dealing must go on online but in Swindon we deal with the more traditional methods of dealing, with a customer being supplied directly or by a runner as a cash business. “Certainly the birthday card we found is still effectively supplying controlled drugs. Money doesn’t have to change hands for it to be an offence.”Generally what we do is seize the item at the sorting office and it gets destroyed and we record it as intelligence.”Police can have difficulty in tracking down the senders of drugs by post. A postal worker sorting cards and lettersCredit:Joe Giddens/PA It has has become a popular method among dealers who use encrypted online market places to sell and deal drugs which are then concealed in harmless-looking packages and cards.Around 800 cases of posted drugs are thought to have been reported in the past year.A Royal Mail spokesperson said: “Royal Mail understands the tremendous harm that illegal drugs cause in the community.“We work closely on the ground with law enforcement agencies, including the police for domestic mail and with Border Force for international mail.“We support these agencies to stop the carriage and delivery of illegal drugs that are ordered on the dark web, We also encourage our postmen and women to report to their managers any suspicious items which we then promptly refer to the authorities.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.