Matthew Fox plays one of the main characters in the serial

But the US show, which focuses on a group of aircrash survivors stranded on a desert island, failed to match its first series debut of 6m viewers.

The double bill, shown on Channel 4 on Tuesday, saw its audience slip to 2.8m after the first hour.

The drama, made by ABC, has been a hit on both sides of the Atlantic and won six Emmy awards last year.

The show commanded more than 20% of the total viewing audience during its two-hour slot on Tuesday, with Channel 4 showing episode one and two back-to-back.

Around 700,000 viewers then tuned into Channel 4's digital sister station E4 to see the third episode of the series.

Ratings winner

The programme became the most successful US debut on Channel 4 when its opening season began last year.

It suffered only a slight dip to 5.9m viewers after two episodes were split by Big Brother.

The double bill, which cost $10m (�5.5m) to make, may have benefitted from having an edition of the popular reality TV show slicing it in half when it was aired last August.

In the US, the drama became a regular ratings winner, with 21m viewers watching the first season finale - up 3m on its debut.