The United States intelligence service used it to spy on military activities in Iraq at the height of the Gulf War.

And soon Global Positioning by Satellite (GPS) could be another weapon in the battle against the beasts of Bradford's sewers - rattus norvegicus - or the common rat, to you and I.

Yorkshire Water contractors Bethell trialled the spy-in-the-sky system on their pest-control vans in November last year.

The idea is that by monitoring every manhole its men visit, out of the 40,000 which lie along the 350,000 metres of Bradford's sewers, Bethell can accurately target the rat hotspots and monitor how many times they have been baited and the success rate.

GPS is a possibility for the future, but on a day-to-day basis the main weapon in Bethall's arsenal is the tried and tested method of sewer baiting.

Mick Goodall, 36, has been a sewer baiter with the company since it began working for Yorkshire Water in April last year.

Once he has lifted a manhole cover up, Mick uses a length of plastic piping to deliver a cup full of Brodifacoum, the latest rat poison, into a dry part of the drain and then adds a pile of sawdust next to it.

He said: "When I come back in a week I check if the poison has gone. The rats won't touch the sawdust but it's to check against wash-offs.

"If the poison and the sawdust have disappeared then it's probably been washed off in a storm or a flood and the poison hasn't been eaten. I'll relay the poison and then come back again."

Brodifacoum is a third-generation rodenticide which is an anticoagulant and makes the rat's heartbeat increase until it finally dies.

Mr Goodall said once the rat had eaten the bait, it would die within a few days somewhere in the sewer network.

John Barrows is YW's contract engineer who liaises with Bethell and has been involved with sewer baiting for more than 30 years throughout the Yorkshire region.

He said the company's total sewer-baiting budget within Yorkshire was £300,000 for this financial year.

"Part of what we are trying to do is to target need and put resources where they are needed," he said. "We are aiming to get about ten per cent of this budget into Bradford, which is about £30,000.

"Since April last year our contractors have lifted about 6,000 manholes in the Bradford district out of a total of 40,000.

"A number of these are repeat lifts so we have probably checked about eight to ten per cent of the manholes in the district.

"We will continue with this process for the rest of this year."

As to the scale of the problem, Mr Burrows remained circumspect.

He said: "Since April 1 last year we have had three call-out requests by Bradford Council to reports of rats in sewers for the whole of Bradford.

"We feel that of course there are rodents about, but the position is one we are comfortable about. We don't see that we are in this crisis situation that has been reported."