Experts think the creature was a Fin Whale. Picture by Noaa

Rob and Lin Briggs were concerned in case the whale came in contact with the hull.

But after altering the Lerryn Lady's route they met stormier seas off the Lizard peninsula.

Mr Briggs, who was suffering severe seasickness, requested assistance, and the Lizard lifeboat towed them back into Falmouth.

I was worried that it might go under the hull and tip us up Lin Briggs

Mrs Briggs said: "It was just an incredible thing to see. It was very calm and eerie and I could hear the blowing noise that a whale makes.

"A bit later on it rose about 100 yards from the boat.

"I panicked and after a few minutes it appeared on the starboard side, much closer.

"I was worried that it might go under the hull and tip us up."

Mr Briggs said: "It was clear that he was longer than our boat and we were concerned that in the event of a collision it could do a lot of damage to the hull.

"It was a beautiful and slightly scary experience because you never knew what was going to happen."

A Cornish expert on marine mammals, Dr Nick Tregenza, said he thought it was likely to be a fin whale.

He said it was quite common for these creatures to come close to shore, but more so in the winter.