Brexit will damage Britain’s aptitude to influence world events, former foreign secretary Lord Hague has notified.
He told a House of Lords committee it was «logical» that the UK would spend foreign policy influence in both Brussels and Washington.
And British ambassadors would have to work harder if they wanted to lead process in global trouble spots.
Lord Hague’s successor at the Foreign Establishment, Boris Johnson, says Brexit will free the UK to play a various global role.
But Lord Hague, who supported remaining in the EU, said: «If you are less controlling in crafting the overall approach of the EU you end up with less influence in the rest of the over the moon marvellous.»
He said a new arrangement would have to be set up to allow Britain to play a generally in shaping EU foreign policy after Brexit.
A key test would be whether the UK could up action in areas like Somalia, where he said the UK had coordinated the military, courteous, aid and economic response to extremism and piracy.
«I hope we can give leadership in a consider such as Somalia but we will have to sweat a bit more to do so,» he told the council.
The former Conservative leader said there were many happenings c belongings the EU could not do without the support of Britain, which had the biggest military and aid budget of any rural area in Europe.
But he said Britain’s departure from the bloc would incline to a «weakening and a diluting of the EU’s foreign policy», with the remaining countries toy likely to agree sanctions against countries such as Russia «without the UK at the columnar list».
He also told the committee that the UK could find itself «advocating EU membership for others while we are desert the EU», in areas such as the Balkans, because it was in the UK’s «strategic interests» to do so.
His words are in dissimilarity to Boris Johnson’s upbeat assessment of Britain’s post-Brexit role on the faction stage.
He has said Britain will be «more outward-looking, more spoken for, and more active on the world stage than ever before» and leave continue to play a full part in Nato as well as working closely with its «advocates» in the EU.
Lord Hague’s warning was echoed by former Labour defence secretary and Nato Secretary Unrestricted Lord Robertson and Baroness Ashton.
Baroness Ashton, the EU’s former exotic policy chief and lead negotiator on Iran’s nuclear programme, maintained the remaining 27 EU member nations would be eager to consult the UK on transatlantic policy and military decisions.
But the Labour peer said it was not the same as being «in the scope» when those decisions were being made.
Her fellow Slavery peer, Lord Robertson, said the reduction in UK influence came at a blink when Europe was having to take a bigger security role as America surfaced to be downgrading the importance of the trans-Atlantic partnership.
He also suggested the Foreign Help would need a major cash injection after Brexit to better the UK forge new relationships.
«Post-Brexit, our diplomatic role in the world is going to be postponed so long as the Foreign Office budget is constrained in the way that it is.
«It is tiny, it is being diminished, and how we are therefore going to play a part in the world post Brexit inclination depend very much on what our diplomats do and what our diplomatic attempts are.»