CHRIS FISHER, EDP Political Editor The stirring up of controversy over inheritance tax by former cabinet minister Stephen Byers is likely to be followed by increasing tension and rancour in Labour ranks in the approach to the party's annual conference, which opens in Manchester on September 24.

CHRIS FISHER, EDP Political Editor

The stirring up of controversy over inheritance tax by former cabinet minister Stephen Byers is likely to be followed by increasing tension and rancour in Labour ranks in the approach to the party's annual conference, which opens in Manchester on September 24.

The principal reason for saying this is well documented. It is, of course, the unresolved issue of precisely when Tony Blair will retire from No 10. The prime minister will be under mounting pressure to give a clear signal at or before the conference. But it is far from inconceivable that he no intention of doing any such thing and that he will leave Gordon Brown to carry on agonising about 'when' and, indeed, 'if'.

Isn't the chancellor's succession to Mr Blair a foregone conclusion? Not in Mr Brown's opinion, I'm sure. His paranoia about this is well known. And just because he's paranoid, it doesn't mean he won't be stopped from getting the job that has been his consuming ambition.

If not Mr Brown, who? One possibility is education secretary Alan Johnson. But the main threat to Mr Brown is home secretary John Reid. He has never endorsed Mr Brown as the next Labour leader and prime minister, and has never ruled out challenging him in an election. As an assertive cheerleader for Blairism, he has often appeared at odds with, and implicitly disapproving of, the chancellor - an impression strengthened by the general knowledge at Westminster that the two men don't like each other much. And while Mr Brown has been away on leave, Dr Reid has been hogging the headlines because of the alleged terrorist plot to blow up aircraft. Deputy prime minister John Prescott has been privately fuming about that, and one can safely assume Mr Brown has been too.

Would Dr Reid really have a good chance of victory if he took Mr Brown on in a leadership election? At this time, 'good' would most probably overstate it by quite a margin. I would expect him to give a good account of himself, to land several strong punches and to get a very respectable vote - but to lose. But quite a powerful case can be made in such contests for expecting the unexpected.

How many people thought at this time last year that David Cameron would be the next Tory leader? Who supposed when William Hague resigned the Conservative leadership that he would be succeeded by Iain Duncan Smith? Michael Foot wasn't the obvious successor to Jim Callaghan as Labour leader, and Neil Kinnock wasn't to him. Before John Smith's death, moreover, it was widely believed that Mr Brown was the likeliest successor.

In addition to their New Labour policy commitment, Mr Brown and Dr Reid have some other strong similarities. They are both Scots, and have both prospered in the pit of festering feuds that is Scottish Labour politics. Each of them, furthermore, has a marked tendency to imply that there is little point in discussing an issue once he's made his mind up.

There are differences as well. Dr Reid, who was in the Communist Party in his youth, has become New Labour's hardest of hard men, and arguably its nearest equivalent of Norman Tebbit. He doesn't take prisoners (speaking metaphorically, of course). And if Mr Blair wants someone to go on the airwaves and defend the indefensible and tell the nation that black is white, his first choice will be the home secretary. There are elements of these characteristics in Brown too, but in his case it's all a bit more subtle and statesmanlike.

An advantage Dr Reid has over the chancellor is a sense of humour. Close friends regret it is less evident now that he is teetotal and has given up smoking, but it is still there. This is a man who won the heart of his second (and present) wife after announcing in his first words to her that he'd been standing on the other side of the room admiring her backside. Can you imagine Mr Brown ever coming out with such a line?

The chancellor has spent so much time preparing his entry into No 10, and has so many supporters in key positions in the Labour machine, that it must be supposed he would be able to summon enough tanks to put down a Reid challenge. But a contest between the two men could be nasty, brutish and not necessarily short. Quite a bit of blood could be spilt in the campaigning, and the fighting might well carry on well beyond the declaration of the result.

That outlook is a further cause for cheer in the Tory camp as David Cameron ponders yesterday's ICM poll in the Guardian putting his party at 40pc, Labour at 31pc and the Liberal Democrats at 22pc.