The elections themselves are within an electoral college consisting of the Parliamentary Party, ordinary Party members and the Trades Union affiliated to the Party. There will be a special conference to hold the election. This is most likely to take place over a weekend.

The key date here is the day of the elections for the Scottish Parliament, Welsh Assembly and local government outside London. This "super Thursday" is on 3 May with the results likely to be finalised late on Friday. The counts take longer as the Scottish and Welsh elections are under proportional representation. The final result is only available when the numbers of "top up" seats can be determined.

The following Monday is a national "Bank" holiday so the earliest Blair is likely to resign is May 8 or 9. The agreed timetable would mean the Conference would be over the weekend of 30 June / 1 July and that is Newsnight's suggestion. My own feeling is that it is more likely to be the following weekend 7/8 July. There are a couple of reasons for this.

The first is a fairly fine one. Labour are expected to do badly in the elections and are likely to lose their majority in Wales. They could even lose the position of largest party in Scotland to the Scottish Nationalists who could get a majority over the current Labour/Liberal Democrat coalition. Blair would not want to be seen to be resigning because of this defeat. As I said it is a fine point as there could be an increasing clamour for it and to go only a week later would make the impression of being hounded from office even worse.

The second is a more minor matter. The changeover normally happens at Buckingham Palace where the outgoing Prime Minister resigns and the new one is invited to form an administration by the Monarch. If you have seen the movie "The Queen", you will recall the scene where Blair became PM. It looks however like the Queen will be in Scotland that weekend as she is holding an official garden party at Holyroodhouse Castle in Edinburgh on that Wednesday. I presume that that will be after a holiday in Balmoral. It is quite feasible for her to travel down to London to enable the "kissing hand" or even for it to happen in Scotland but Brown would not like either. It will remind the public of his origins at a time when he is emphasising his "Britishness". The following week however she is holding a garden party at Buckingham Palace so would naturally be in London. That would make Blair's last day in office Monday 9 July.

Brown's budget contained a number of environmental measures:

Home front

The Chancellor promised to encourage cuts in emissions from homes, which he said accounted for a quarter of the UK's total carbon output, including:

    * grants worth £300-£4,000 for pensioners installing insulation and central heating in their homes;
    * consultations with banks and building societies to develop new mortgage products for investment in energy efficiency;
    * a zero rate of stamp duty to be paid on new homes costing less than £500,000 which have a zero carbon footprint till 2012;
    * £6m extra for the Low Carbon Buildings Fund; and
    * a push to find ways of making it more lucrative for people to sell energy generated by systems such as solar panels back to the National Grid.

Car tax

As for transport, Mr Brown announced that fuel duty would go up 2p a litre in 2007 and 2008 and 1.8p in 2009 - although this year's increase is to be delayed till October.

The rise in VED (annual road tax) for Band G cars - which include not only 4x4s but also some large people carriers and estate cars - was accompanied by a £10 rise for Band F vehicles, the next most polluting cars.

But while the least polluting Band A cars will continue to pay no VED, the next cleanest in Band B will see their rate cut to £35 from £50 for diesels and £40 for petrol cars.

And biofuels, which Mr Brown said helped fulfil the government's obligations on renewable fuels, would have their 20p a litre duty reduction extended to 2010, with the 40p a litre reduction for biogas extended to 2012.

Mr Brown said he had asked Sir Nicholas Stern - author of the Stern Review - to work with Professor Julia King of Aston University on developing "the next generation of low and no carbon vehicles".

In other environmental taxes, the Chancellor said he was raising landfill tax from its current rate of £24 a tonne by £8 a year till 2011, and boosting the aggregate tax which penalises quarrying from £1.60 to £1.95 a tonne.

The Climate Change Levy on businesses is to go up in line with inflation from April 2008 and is to be simplified, the Chancellor said.

International action

As for the international dimension, Mr Brown noted that the EU had made a binding commitment to cut carbon emissions by 20% below the 1990 level by 2020.

The UK, he said, had reached a range of deals on environmental issues such as biofuels and clean coal with countries from Brazil to China.

And he promised £50m to a 10-country initiative to protect rainforests in Central Africa, as well as £800m to the government's Environmental Transformation Fund.

These are clearly designed to present himself as greener than the Leader of the Opposition. He ridiculed several suggestions for environmental taxes that he had put forward, notable Value Added Tax on domestic air travel. This would not form much of a deterrent as businesses can reclaim it.