Helen Andrews was one of the youngest at Bletchley Park when she arrived from South America.

A brilliant mathematician at 17, her family had been told that she had a place at Cambridge.

She travelled back to the UK on a lightly guarded Atlantic convoy of ships which took almost four weeks.

Three ships in the convoy were sunk by U-boats - as the convoy was not allowed to stop, she witnessed many women and children drowning.

When she docked at Tilbury, she was invited to the captain's quarters, where she was told: "A man is waiting for you. Get in his car and don't ask any questions".

She was driven to Bletchley, not Cambridge. At 92 she has only just started talking about her experiences.