A man caught trying to record young girls changing at a leisure centre was found with a stash of 4,500 indecent images of children at his home.

Martin Fitch, 39, was jailed for four years at St Albans Crown Court today (Tuesday) after admitting 14 charges of downloading the images and possession of a total of 4,550 pictures - a number classed at level five, depicting the most horrific sexual offences against children.

Fitch was arrested after complaints were made he was trying to use his phone to video young girls changing at Woodside leisure centre in Watford on May 2, 2009.

DC Dave Miller from the Local Crime Unit in Watford said: "It was recognised that Martin Fitch's criminality was escalating. This was reflected by the sentence he was given and I am pleased that the serious nature of his crimes has been acknowledged."

Fitch, whose address was given as Aylett Nurseries in North Orbital Road, St Albans, was caught acting suspiciously, putting his phone under a number of partitions in the changing rooms.

Daniel Murray, defending, said after an unrelated conviction in 2005 Fitch had been diagnosed with Aspergers, and asked for an adjournment for a mental health assesment.

However, there was no record of Fitch receiving treatment or any medication and The Honourable Justice Jeremy Cook rejected the application, adding that only a custodial sentence was appropriate.

Mr Murray accepted his client must go to prison, but said in mitigation Fitch was a “vulnerable” individual, who had not been able to form any relationships.

An example of his naivety was how he showed his phone with a camera on it to his probation officer, when a condition of bail was that he did not have a phone, said Mr Murray.

Fitch was estranged from his family, had lost his job as a result of the charges and now relied on benefits.

Fitch will serve an extended probation period when released from the four-year sentence after Mr Justice Cooke noted he was a “danger to the public”.

He said: “There is no alternative other than an immediate custodial sentence.

“These matters came to light following an incident at a leisure centre, where you were found to be taking photos under cubicle doors of girls in the changing rooms.

“That is not the subject of these matters, but it led to a search of your home and 4,550 indecent images of children were found in two computer towers.

“The pre-sentence report says you are a high risk of serious harm to children through committing serious offences.

“Therefore, I have no option but to send you to prison with an extended term of licence.”

Fitch was told after release from prison he will remain under supervision by probation for three years.

He must sign on the sex offenders’ register and was given a sexual offences prevention order of which one of the conditions bans him having a camera.

A forfeiture and destruction order was placed on the items seized by police.