Just to report that both dongles are now working with very little effort at all.

I just installed usb-modeswitch and both dongles worked without any hassle at all. The Virgin Mobile Alcatel one just plugged in, was trivial to set up and worked.

The Belgian one was a *little* more involved but not bad:-

I bought an unlocked Hauwei (3) dongle one Ebay for £19.99

I got a Mobistar pay-as-you-go SIM in Belgium for 15 euros

Plugged said SIM into the dongle and it connceted but would only access the Mobistar site saying it had run out of credit.

I then realised I had to 'enable' it by putting it in my mobile phone and texting 'start' to specified address.

... and now the Mobistar dongle is working too, hence this message.

It was all rather less painful than I feared.