UK mobile firm EE has recalled a portable charger it had given away after a medical student was left with severe burns when using one.

EE said that it had identified five incidents where its Power Bars had overheated and as a result was recalling one of the batches.

That amounts to about 500,000 units, according to the firm.

As a gesture of goodwill it will be offering affected customers a £20 voucher to spend on accessories.

In a statement, the firm said: "We have identified a very small number of incidents where Power Bars have overheated, all of which relate to batch E1-06 (written as Model:E1-06 on side), and could pose a fire safety risk.

"We are therefore recalling this batch, and requesting customers to stop using the Power Bar and return them to a local store at their earliest convenience."

Medical student Katy Emslie, from Aberdeen, suffered severe burns when her phone charger exploded and set fire to her bedroom floor.

EE began giving away the smartphone charger to every customer in April. It also let customers trade in a flat one for a fully charged one.

The gadget has a charging indicator that shows how much charge is left on a mobile and will allow users to completely charge a dead smartphone battery once.

The device was rolled out after research suggested that nearly 60% of smartphone users found that their phone batteries did not last for a full day.

EE was swamped with requests for the charger and estimates that there are now 1.5 million in circulation. It told the BBC that only the batch identified was affected.