Cabinet Minister Ruth Kelly is resigning amid speculation that she could not reconcile her conscience with the Government’s controversial embryology Bill.

According to The Daily Telegraph, Downing Street is linking Miss Kelly’s departure to her religious objections to the contents of the Human Fertilisation and Embryology Bill, which has been strongly opposed by pro-life groups.

The Bill contained a number of contentious issues including saviour siblings and animal-human embryos.

When the Bill was due for its final vote in July, Miss Kelly was criticised for telling Labour whips that she would be attending a meeting in Brussels instead.

However, the Government postponed the final vote until the autumn, when all Labour MPs would be expected to vote in favour of the entire contents of the Bill.

Many observers have attributed Miss Kelly’s decision to leave the Cabinet at least in part to her objections to the Bill, although the explanation offered to reporters was that she wanted to spend more time with her family.

She said: “This is a decision that has been taken absolutely, completely for personal reasons. I owe it to my family to start putting it first.

“Being in frontline politics and bringing up four children and being a constituency MP, it has not been easy all the time. I do think it is time just to take a step back and repay the support that [my family] have given me over the years.”

Miss Kelly was also understood to have clashed with the Government over the Sexual Orientation Regulations by siding with then Prime Minister Tony Blair in calling for exemptions for Roman Catholic adoption agencies.