While it is difficult to put a figure on the reptiles and amphibians which are on the loose, officials involved in re-capturing and finding new homes for them estimate a rise of between 150 and 200 per cent in the last three years.
There are three main reasons for the upsurge in summer urban sightings of snakes and reptiles, according to wildlife experts.
Although the animals are relatively content to snuggle up in the warmth of their tanks and boxes in the winter, when the weather changes, like humans, they want to be out in the sun. Heavy, hot weather make smakes humans lethargic, but for creatures more used to hotter environments, it simply makes them more active.
And just as traditional pets like dogs and cats are dumped in the street by owners going on holiday, so are the more exotic pets. Many of these owners also discover that they cannot cope with the financial and practical problems associated with keeping these specimens.
Instances of reptiles and amphibians turning up at unlikely places may seem like urban myths, but they are recorded by bodies such as the RSPCA and the British Reptile and Amphibian Society (BRAS).
In Leytonstone High Street, East London, a man about to sit down on a public toilet made a sharp exit after seeing a snake sticking its head out of the bowl. It was traced by the police to a private collector. The BRAS chairman, Mick Powell, said: "It was a Prairie King snake which had crossed four main roads to get there. The guy on the loo got quite a shock."
In just one day last week Mr Powell collected a Californian King snake, which can grow up to 6ft, after it had turned up at a house in Ilford, Essex, and a 3ft Western Hognose in a garden at nearby Dagenham. He was also making arrangements to pick up an anaconda, which can grow to 12ft, from Kent. At present he is keeping 15 recaptured snakes at his home in Dagenham, while new homes are found for them.
Mr Powell said: "There is no doubt we are finding more and more escaped reptiles and amphibians. In l994 I had to deal with around 30 snakes, lizards and turtles. Last year it was around 100, and so far this year it's just over 50."
RSPCA inspector Mark Martin has to routinely deal with exotic fauna. Four weeks ago at a house in Enfield, north London he found scorpions which, the Natural History Museum later declared, were Buthotus Tamulus, one of the most venomous in the world. He has also recently picked up a poisonous and aggressive 6ft Montpellier snake outside Walthamstow station, in north-east London, and an escaped Simoloyan Milk Snake at a pub in Highbury, north London.
Mr Martin has found security to be a major problem. He said: "I have actually seen spiders being kept in Tupperware boxes, and then the owners have been surprised when they simply climbed out. It is relatively easy in many cases for animals like snakes to get out, and that is what they want to do in the summer.
Many in the animal welfare field believe the licensing systems for both buyers and sellers need to be re-examined. Under the Pet Shops Act of 1951, shops do not need to have specialist knowledge of exotic creatures to stock and sell them, and thus, in many cases, they cannot pass on relevant information to customers.
The shops can get licences as long as they can satisfy that they do not pose a health hazard to the public.
Customers do not need a licence under the Dangerous Animals Act to keep non-venomous snakes, such as pythons. Even when acquiring reptiles covered by the Act, such as cobras, they do not have to produce the licence. The actual cost can vary between pounds 50 and pounds 200 a year, depending on local authorities, and the police perception is that many collectors are flouting the law by simply not getting licences.
Veterinary surgeon Martin Lawton, one of the leading specialists in exotic species medicine, said: "The main problem is a lack of knowledge both by pet shops and customers.
"Most people do not know what they are taking on. There is the initial cost, for example it can cost up to pounds 200 for a vivarium for turtles, and then there are vets' fees. There is also the cost of the food. You cannot just go out and get a can of Whiskas for an anaconda - specialist food is needed.
"A lot of these pets could also outlive their owners, that's the reason we advise they put them in their will. A python can live to 20 years, and something like a spurred thigh tortoise, which have become popular, can live to 100."
RSPCA inspector Mark Martin said: "A lot of people think that reptiles are hassle-free pets. "They don't have to be taken for walks like dogs, or scratch furniture like cats. So when they realise just how much care and attention is needed to look after things like snakes they get quite a shock."