Robbers in Balham have revealed themselves as amateurs after botched raids on two shops.

The latest was at the post office in Cavendish Road, where robbers failed to start their getaway car.

The four thugs threatened staff with a knife at 6am on Tuesday and managed to take some money and shop items.

However, their blue Fiat Punto refused to take part, and they were forced to flee on foot.

Two of the suspects ran towards Hydethorpe Road and the other two towards Haverhill Road.

Detectives, who described the suspects as four black men aged between 20 and 25 and wearing dark clothing, are appealing for witnesses.

The week before, six robbers embarked on an attack on Sainsbury's, Balham High Road.

The men, armed with an iron bar, and rounded up staff, none of who knew how to get into the safe.

Detective Inspector John McFarlane said: "They realised they weren't going to get into that safe, and then they fled. But they behaved very intimidatingly, and some staff were very upset."

The men, who were in their late teens or early 20s, went away with just a mobile phone.

The incident happened at 5am on February 6, when the store was taking a delivery.

The men entered the yard area in a silver vehicle, believed to be a Citroen.

Police are appealing for witnesses who may have seen the suspects, who were wearing dark hooded clothing.

A spokesperson for Sainsbury's said: "The safety of customers, visitors to our premises and colleagues is of paramount importance to us and we are working with the police to assist them in their investigation in any way we can."

If you have information on the Sainsbury's incident, please call DC Adams at the Priority Crime Unit Wandsworth police station on 020 8247 8807.

To give information about the post office incident, call Barnes Flying Squad on 020 8247 7931.

To report any information and remain anonymous, you can call Crimestoppers, free, on 0800 555 111.