I am now told by the JESS secretariat that the Report WILL (their emphasis) be published next week.  Watch this spot.
Well, despite the JESS Secretariat's firm statement, the Report was not published.  I have now been told that,

"Contrary to the information I had last Friday (or indeed for most of this week), we are now going to coordinate the JESS report publication with the release of two other statements from the Minister.  This was trailed at DTI questions in Parliament yesterday"

Hansard reported it thus:

7. Mr. Mark Lancaster (North-East Milton Keynes) (Con): If he will make a statement on the current and future diversity of the UK's energy supply. [67728]
The Minister for Energy (Malcolm Wicks): Securing reliable supplies of energy in the medium and long term is one of the key considerations of the Government's energy review, which I am leading, that will report to my Secretary of State and the Prime Minister in the early summer. Details on the diversity of the UK's energy supply will be contained in the latest report by the joint energy security of supply working group, which, I am pleased to tell the House, will be published next week. In addition, I will make written statements to the House soon about the past winter's experience and on the key issue of planning needs for new gas import and storage infrastructure.