THE RAF's new fleet of Typhoon Eurofighters, due to begin entering service next year, could be left defenceless because of the proposed closure of the Bishopton munitions plant outside Glasgow.

The Ministry of Defence is buying 232 Typhoons for #39m apiece. Peak production of the multinational collaborative aircraft is expected to support 16,000 high technology and up to 80,000 dependent jobs in the UK. The #40bn project, already years behind schedule, involves Germany buying 180 of the aircraft, Italy 130, and Spain 87.

However, documents obtained by The Herald show British Aerospace Systems, the UK's biggest arms contractor, has discovered the propellant charge needed to release the Typhoon's Skyflash air-to-air missiles is made exclusively at the threatened Scottish site. The company has also failed to persuade the US firm Olin, manufacturer of similar propellant for the American services, to alter its own manufacturing process to conform to British and RAF safety standards.

The propellant, packed into a cartridge, powers the release mechanism for missiles and for underwing fuel tanks used to increase a fighter's operational range.

The missiles and tanks have to separate cleanly from the fighter at speeds of up to 600 knots to avoid them tumbling back into the wings or fuselage.

The Bishopton propellant powers the current Cartridge Ejector Release Unit (CERU) for the Typhoon and for the Tornado ground-attack and fighter squadrons it is intended to replace.

Internal BAe Systems memos indicate a number of managers began to realise the scale of the problem in March this year.

One suggestion was that Royal Ordnance, the subsidiary which owns Bishopton, buy the CERU propellant from ICI Explosives at Ardeer in Ayrshire. The Herald understands, however, that ICI has closed its production line and considers it uneconomic to reopen it for a relatively small order.

A BAe Systems spokeswoman confirmed yesterday the company was ''actively seeking an alternative source of supply for CERU''.