The freed hostages, along with the Sierra Leonean army officer, are now safely aboard the British naval vessel Sir Percival in the harbour of the capital Freetown.
The UK Ministry of Defence said another British soldier had been seriously injured and 11 suffered light wounds.
But the six British soldiers and a Sierra Leonean officer were all rescued unhurt after the dawn raid on the militia camp in the Occra Hills east of the capital Freetown.
UK Prime Minister Tony Blair paid tribute to the 150 troops, on board five helicopters, who carried out the mission, which rescued the men, who had been held since 25 August.
'Mock executions'
Eighteen members of the West Side Boys militia - 15 men and three women - have also been captured, including the group's leader "Brigadier" Foday Kallay.
The raid was launched after the West Side Boys made repeated threats to kill the captives and carried out "mock executions".
Defence Secretary Geoff Hoon said the decision to move in came after a breakdown of talks with the group, and following reports they staged "mock executions" on the British soldiers, all members of the Royal Irish Regiment (RIR).
Blair pays tribute
Mr Blair said his thoughts and prayers were with servicemen's families.
He said: "I cannot pay high enough tribute to the skill, the professionalism and the courage of the armed forces involved.
"Inevitably, in such an operation as this, there are casualties. The details of these will be given out later."
The freed hostages, along with the Sierra Leonean army officer, are now safely aboard the British naval vessel Sir Percival in the harbour of the capital Freetown.
At the RIR's headquarters in Ballymena, County Antrim, there was intense relief, but the celebrations were tempered by news of the rescuers' casualties.
General Sir Charles Guthrie, chief of the defence staff, saide there had been "significant resistance" from the West Side Boys.
"They fought very hard and there were women among the fighting, some of whom may have been among the casualities."
The rescue operation centred on a militia camp in the Occra Hills, situated on both sides of a 300 metre-wide creek surrounded by swamps.
The raid began at first light on Sunday as men from the 1st Battalion the Parachute Regiment, along with RAF and Royal Navy forces, began their assault on the camp outside Freetown.
Mr Hoon said a military operation was only authorised after negotiations were seen to be failing.
He said the West Side Boys had received a satellite telephone, food and medical supplies to meet their demands.
But at the last meeting with Brig Kallay the demands had got unreasonable.
"He was pressing for quite unreasonable and unattainable political concessions," said Mr Hoon.
Blair authorised mission
A Downing Street spokesman said Mr Blair authorised the troops' move on Wednesday, and gave the final go-ahead for the mission to free the soldiers from the Royal Irish Regiment on Saturday afternoon.
A Ministry of Defence spokesman told BBC News Online the Sierra Leone Government and the United Nations had been kept fully informed.
Five of the British soldiers were released last Wednesday and are being returned to Britain this week.
But the released soldiers' senior officers are understood to be no closer to understanding how their group was captured in the first place.
It appears they may have become caught up in a local political dispute.
The West Side Boys included former government army troops who said they want the peace agreement signed last year renegotiated.
The elected and British-backed Sierra Leone government publicly rejected this demand, saying it would encourage more of the lawlessness which has plagued the country for a decade.