Sir Jon Shortridge stepped down as permanent secretary in April 2008
Former top civil servant in Wales Sir Jon Shortridge has said the role of the Wales Office should "wither away".
He said he expects Welsh ministers to deal more directly with Whitehall, as devolution develops, rather than via the Welsh secretary of the day.
Sir Jon also criticised last year's launch of the UK government's "Building Britain's Future" policy proposals.
He said many of the plans related only to England but he believed UK ministers had simply chosen to ignore this.
Sir Jon, 62, was the assembly government's first permanent secretary and led the civil service in Wales for nearly a decade, until 2008.
He was giving evidence to MPs on the Welsh Affairs Committee, which was meeting in the Welsh assembly building in Cardiff Bay as part of its inquiry into the relationship between Wales and Whitehall.
Sir Jon said: "My own personal view is that, as the settlement matures, the engagement will be with individual departments of state, policy departments, and that the need to have a Wales Office, which in part has a role for brokering relationships between policy departments, should just wither away."
In his written submission, Sir Jon said he had "always seen the Wales Office as having a temporary role".
"In the early years of devolution it was important that there should continue to be strong Welsh representation in Whitehall and an associated cadre of civil servants who could advise on the handling of Welsh issues," he said.
"But as the Welsh settlement matures the role of the Wales Office, in my view, becomes all the more anomalous.
"Ministers and civil servants in Wales, understandably, want to be able to deal directly with their counterparts in the relevant Whitehall policy department.
"Having to deal with the Wales Office as well can become a complication too far.
"In my view, devolution in Wales will have come of age when the prime minister of the day feels that separate departments for Wales, Scotland and Northern Ireland are no longer needed," Sir John added.
He also laid out a series of difficulties, both current and ongoing, which he believed were hampering relations between Whitehall and Wales.
They included cases of Whitehall not making it clear in announcements when policies applied to England only and also failing to notify the assembly government of major announcements in advance.
Sir Jon was particularly critical of last year's launch of the UK Government's flagship set of policy proposals entitled "Building Britain's Future".
He said many of the policies were relevant only to England, but that he believed UK ministers had simply decided to ignore this.