Tony Blair delivered a thinly veiled warning to Gordon Brown yesterday that a future lurch to the Left by Labour would place the party in opposition for years to come.

Addressing young Labour activists at their conference in Glasgow, the Prime Minister also appeared to cast doubt on whether Mr Brown was inclusive enough to lead Labour in the same manner as he had.

Just as the Chancellor yesterday expanded his group of close political aides by appointing the Chief Rabbi’s daughter as his eleventh special adviser, Mr Blair was hinting that he needed to break out of his tight circle of allies and embrace “Big Tent” politics.

“Political parties,” Mr Blair said, “cannot be led by any one person but by a broad movement of people prepared to stand up and have the power to change people’s lives and recognise that politics has a liberating power for humanity.”

The Prime Minister, who did not mention his probable successor by name, reminded his audience that Labour had won three terms in power because it had been prepared to change and was no longer seen by voters as a prisoner of the Left.

Then in words that will be seen as a direct admonition to Mr Brown, the Prime Minister said: “If you want to carry on governing, you have to carry on changing.”

He told his audience that his “forces of conservatism” conference speech in 1998 had been widely misunderstood because it was not solely an attack on the Conservative Party, but also a criticism of conservatism, with a small “c”, of all types.

He added: “We only came to this position of three terms because we had the determination to make the changes necessary to become a governing party. We must never return to the days when we were comfortable in opposition.

“Retaining power is not about sacrificing principle. Retaining power is actually the only way to implement principle. What we have to do now is work out what are the next stages of this.”

Mr Blair also returned to the theme that has dominated his visit to Scotland — the future of the Union with England — and took head-on the claims by Nationalists and others who say that the bond between the two countries has served its purpose and should end.

The partnership between Scotland and England, he said, should not be portrayed as two countries “huddling together for safety” but as a source of strength for both countries.

He appealed to Scottish voters to support the Union at the Holyrood elections in May, not out of fear of separation but because they were excited about greater prosperity through a modern Union.

The Prime Minister’s remarks underlined the change of approach by Labour towards May’s election that has emerged this week. Instead of issuing dire warnings to Scots about the dangers of independence, the party appears now to be stressing the positive dividend to Scotland of the Union.

In London, Gordon Brown’s appointment of Gila Sacks, further expanding his council of economic advisers, was seen as another stage in his preparations for leadership. Her father Jonathan, the Chief Rabbi, is close to the Chancellor and has described their relationship as one of his “loveliest friendships”.

The Treasury denied cronyism and said that Ms Sacks, 24, had been appointed because of her experience in strategic development while working for a Jewish charity.

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