Gordon Brown arrived home from South America yesterday to another scandal surrounding his Home Secretary.

Starting a week that could determine his political fate, the last thing he needed was to be confronted with doubts about a senior Cabinet minister whose promotion was a surprise and a gamble early in his leadership.

Mr Brown rated Ms Smith in her previous jobs and likes her. His instinct has been and remains to stand by her. But yesterday’s revelations have left her in a much weaker position. She clearly knew nothing about the television bill and the “additional features” on it.

It is easy to sympathise with her. But an investigation over the allowances claimed on a home that she shares with her sister is continuing. That is serious enough for someone in her position, although there is no evidence that she has done anything wrong. But yesterday’s disclosure has added a sense of embarrassing farce. And when a politician is no longer taken seriously he or she can no longer be effective.

This week of all weeks, when London faces the threat of violent protests, the Home Secretary will have plenty of work on her plate to take her mind off domestic matters. She was “mortified” at being told what had happened, and probably even more mortified by the awkward appearance on television of her hapless husband to apologise.

It may be that Mr Brown planned to move Ms Smith in his final big reshuffle. A big debate is going on about whether that will come after the June elections, when Labour looks set to fare dismally, or in the autumn before the party conference.

Ms Smith’s difficulties may mean that Mr Brown will have to act earlier than he would have wished. Many MPs are probably very much on edge. More revelations are in the pipeline. Who knows what other unpleasant shocks lie in wait? Ms Smith’s future will be settled one way or the other. Her predicament and that of other MPs must lead to the end of the current utterly discredited expenses system.

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