MI5 and MI6 jointly run a three-strong team of experts dedicated only to researching and providing training in secret writing and invisible ink, according to a controversial book by former intelligence agent Richard Tomlinson.

An attempt by the government to delay publication in the British media of the contents of the book, The Big Breach, finally collapsed in the court of appeal yesterday.

The book reveals that British intelligence's favoured "offset" method of secret writing entails jotting down notes with a Pentel, then pressing the writing on to a clean sheet of paper, thereby transferring an invisi ble chemical to the clean sheet - which reproduces the written message when swabbed with the developing fluid that Tomlinson says he carried disguised as a bottle of Ralph Lauren toilet water.

The technique was discovered accidentally in the 1980s when a secret message from Russia was being developed in London and found also to contain Cyrillic script from the surface of a letter it had been pressed against in the post. "The technician realised that the Kiev address must have been written with a commercially available pen. If that pen could be identified, it would be a superbly elegant, simple, and deniable secret writing implement," Tomlinson writes.

"MI6 mounted a systematic worldwide search for the pen and every MI6 station was asked to send a secretary to the local stationery store and buy every make available. It took many weeks to identify the magic pen: the Pentel rollerball. Offset is now used routinely by MI6 officers in the field."

More glamorous accessories are kept in a spy's false-bottomed briefcase, according to the rogue agent. Ordinary cassette recorders are modified to utilise the normally unused parts of the magnetic tape for clandestine recording, and hidden spaces in floppy disks are used to secrete wordprocessing systems in laptop computers.

On his arrival as an agent in Bosnia in 1993, Tomlinson says his predecessor handed him a fountain pen which fired a 7.65mm bullet when the cap was turned. "Here, take a look at this, one of [Bosnian Serb leader Radovan] Karadzic's bodyguards gave it to me," Tomlinson says he was told.

The specialised army, Royal navy, and RAF back-up sec onded to work with MI6 also means the Secret Intelligence Service is equipped with a mini-submarine, a Puma helicopter, a Hercules transport aircraft, and a crack unit of SAS troops based in Hereford known as the "Revolutionary Warfare Wing", Tomlinson writes.

The RAF supplies 10 pilots known as the "SD flight". The army and navy contributions are known as "the increment" and are trained in sabotage, guerrilla warfare, VIP protection, and use of explosives.

The Hercules C-130 transport aircraft is used for ferrying large items of equipment to MI6 stations abroad, while the naval staff, based at Poole in Dorset, operate MI6's mini-submarine - "about the length of two cars. The pilot and navigator sit astride the cylindrical forward hull dressed in dry suits and breathing apparatus. The rear half of the craft flattens into a passenger compartment which is just large enough to carry four persons packed together like sardines."