By political correspondent Nick Assinder

The job of home secretary is always likely to be one of the most demanding in government.

It is not only a hugely political post, but it carries with it judicial responsibilities which must be met without any regard to politics.

It is a fine line that has landed Jack Straw with a series of highly sensitive decisions within a short space of time.

The most controversial has been over the future of former Chilean dictator General Pinochet.

But he has also faced decisions over alleged Nazi war criminal Konrad Kalejs and cold war spy Melita Norwood.

After 15 months of wrangling, Mr Straw is likely to release General Pinochet to return to Chile because he is deemed unfit to face trial.

Apparently his condition has worsened dramatically since last October and he would be unable to follow any court proceedings or make any coherent statements on his own behalf.

No evidence

The announcement has come hot on the heels of Mr Straw's decision to allow Mr Kalejs to leave Britain after police decided there was not enough evidence to prosecute him.

He left the country after being warned that he was facing deportation.

Earlier, Mr Straw sparked anger by failing to prosecute a former KGB spy, 87-year-old Melita Norwood, who admitted passing nuclear bomb secrets to the Soviets at the height of the Cold War.

The cases led shadow home secretary Ann Widdecombe to claim that Mr Straw did not have a grip on his job and had taken "many conflicting decisions".

He had originally arrested General Pinochet while he was in bed recovering from an operation, had let Mr Kalejs walk out of the country before the police investigation had even started and had taken no action against a cold war spy, she claimed.

Mr Straw was also attacked by veteran left-winger Tony Benn who suggested the decision on General Pinochet was a political one and claimed it would undermine the government's ethical foreign policy.

And there are certainly fears that, while New Labour was eager to promise an ethical dimension to its policies before the election, putting that into practice has proved far more difficult.

By the book

But Mr Straw has insisted throughout that he has acted "by the book" in all three cases.

He has a duty to take the independent medical advice on General Pinochet into account when making his decision on extradition, he could not have stopped Mr Kalejs leaving because there was no evidence and no one had sought extradition, and he had been advised by the solicitor general that there was no way a prosecution against Mrs Norwood could succeed.

Unpalatable as some of those decisions may have been to the home secretary, he would have faced fierce criticism from all sides if he had overruled such advice.

He had previously won praise from many for arresting General Pinochet but criticism from others, notably former prime minister Margaret Thatcher, for refusing to send him home to Chile.

He has also been praised in the Commons for allowing the British courts, during the battle to extradite General Pinochet, to rule on whether a former sovereign can be granted immunity against crimes committed in office.

The Law Lords finally ruled in November 1998 that no such immunity could be granted.

To a very large extent, home secretaries are always going to be caught between rival factions in such cases.

The only course open to them is to do their utmost to stick to the rule of law and live with the flak.

That is what Mr Straw insists he is doing - but he is certain to face a lot more flak before the Pinochet case is over.