Supermarket groups Tesco and Asda have promised to probe claims of worker abuse at factories in Bangladesh where their clothes are made.

The latest allegations follow investigations by The Guardian newspaper, which revealed employees are being forced to work up to 80 hours a week for as little as 4p an hour.

The newspaper report also said workers were refused access to trade unions, claiming four colleagues had been sacked for trying to organise a union in the last month.

Tesco said it had done all it could to ensure "high standards and good conditions" in the country, while Asda said any abuse was "unacceptable."

The latest allegations follow similar claims made in December last year by War on Want in a report titled 'Fashion Victims,' which was based on research among workers in six unnamed factories in Bangladesh's capital Dhaka.

The charity claimed that bargain retailers such as Primark, Asda and Tesco "are only able to sell at rock-bottom prices in the UK because women workers in Bangladesh are being exploited."