Yep, just got a reply now from Handtec.co.uk (what are they doing up at this time!):
"Thank you for your email,
The HTC Desire sim free release date has now been slightly postponed, this is in response to confirmation from HTC that the release of this product will not be the previously mentioned 29th March but will be anytime between now and the 7th April,
I do apologise for this delay however this will not only affect Handtec however will affect all UK retailers as this has been imposed by HTC directly, however once the stock arrives we will promptly dispatch the goods,
Please advise if we can assist you further."