Tropical storms Felix and Dean - which hit holiday resorts in Mexico rather than the United States - have so far failed to put a dent in the finances of the venerable City institution.

However, boss Richard Ward is counselling caution, saying: 'There's no guarantee at all that these conditions will continue. Far from it.'

The windy season has barely begun, and there is still a chance that a massive twister could hit America with the force that regularly flattens huge tracts of Florida.

But it is a measure of the Lloyd's market strength that Ward reckons it could withstand a catastrophe that wrought more than £50bn worth of damage.

Lloyd's proved impervious to the monsoon summer floods that caused so much damage across Britain and put a huge dent in the finances of the mainstream insurers.

It managed to dodge the effects because it does not offer household cover. And it was largely unaffected by the gales that tore through mainland Europe earlier in the year.

'We've had some near misses and that makes me a little reserved and cautious about what might be out there for us in the rest of the year and in 2008,' chief executive Ward admitted.

Lloyd's made a profit of £1.81bn in the first half, up 34% on a year ago.

The lack of a major catastrophe was obviously one major factor behind the strong showing - though underwriters were also able to keep prices high.

Figures were also flattered by the release of cash from reserves no longer needed to pay claims.

Underwriters are also becoming more efficient. The market's combined operating ratio, which measures cost as a proportion of revenues, improved to 82.9% from 86%.

Ward reported some pressure on prices, particularly the amount charged for aviation and motor cover, but premiums are coming down from historic highs.