Labour have called the nomination of Lord Hill as the UK's next European Commissioner "a shambles".
David Cameron's choice has come under further scrutiny after it was announced Lord Hill would be selling his shares in a lobbying firm to avoid accusations of a conflict of interest.
Shadow Europe Minister Gareth Thomas said: "David Cameron's approach to Europe goes from bad to worse."
"After his complete failure to stop Jean-Claude Juncker becoming Commission president this shambles will not help in rebuilding our influence to secure crucial reforms."
Britain's nominee for the European Commission is to sell his shares in a public relations and lobbying firm to avoid any suggestion of a conflict of interest.
Lord Hill holds shares in Huntsworth plc, which bought the company he founded, Quiller Consulting, in 2006.
Video: Lord Hill: I would have been 'mad' to turn down EU job
Downing Street does not seem to believe the shareholding does create a conflict of interest, pointing out that Lord Hill has been a minister for four years and sits in the Cabinet.
That raises the question: 'Why are shares in a lobbying firm OK for a British Cabinet Minister, but don't look good for a potential EU Commissioner?"
Lord Hill, David Cameron's nominee as Britain's new European Commissioner, said he would have been "mad" not to accept the Prime Minister's offer.
Asked whether he was a eurosceptic, the former lobbyist said he was "not one for names or badges or boxes" but that he wanted to reform Europe to make it stronger and serve citizens better.
Mr Cameron is in Brussels tonight in a bid to secure one of the key economic portfolios in the European Commission for Britain.
Read: Cameron to seek top European job for Lord Hill