Whistl (formerly TNT Post UK) is a postal delivery company based in Marlow, Buckinghamshire, England.

[1] Whistl provides services across business mail, parcel delivery, order fulfilment, contact centres and Doordrop Media both in the UK and internationally, processing around 50% of bulk business mail in the United Kingdom,[2] handles more than 3.6 billion items a year and has over 1.5 million square feet of fulfilment space across the UK.

The company began delivering in West London in April 2012, later rolling out its end-to-end service in Manchester and Liverpool.

[4] In May 2015, Whistl announced that it would suspend door-to-door deliveries in London, Liverpool, and Manchester after the private equity investor LDC, a division of Lloyds Bank, decided not to fund further expansion citing "ongoing changes in postal market in the United Kingdom dynamics and the complexity of the regulatory landscape" and an attempt to stem losses.

In December 2020, Whistl strengthened its order fulfilment offering by acquiring Clientbase,[11] a privately-held company based in Paignton, Devon, which offered fulfilment service for home-shopping companies, including picking and packing, 140-seat contact centre capability, warehousing, returns handling and delivery.