Android / T-Mobile HTC not connecting on 3G

After returning from two weeks' holiday where I'd used only Wi-Fi and not 3G at all, the latter just would not connect.

The resolution is to set up a new APN:

How to configure Internet Settings on your HTC Desire HD.

    Press the Menu key
    Tap on Settings
    Tap on Wireless & Networks to select.
    Scroll down and tap on Mobile networks
    Tap on Access Point Names to select.
    Press the Menu key
    Tap on New APN
    Tap Name then enter T-Mobile Internet select OK
    Tap APN then enter general.t-mobile.uk select OK
    Tap Username then enter t-mobile select OK
    Tap Password then enter tm select OK
    Tap APN type then enter default select OK
    Press the Menu key
    Tap Save
    Press the Home Key

Your phone is now ready for use