Britain's top diplomat in Pakistan met Prime Minister Yousuf Raza Gilani on Wednesday to "calm political tensions" after dozens of people were arrested ahead of an opposition rally.
British High Commissioner to Pakistan, Robert Brinkley, held talks with Gilani as the mission said it was "very concerned" about the reported arrests.
"Robert Brinkley met the prime minister today in a bid to calm political tensions," British High Commission spokeswoman Jennifer Wilkes told AFP.
The high commission said it was "very concerned by reports of arrests of opposition politicians and activists in Islamabad and across Punjab province."
"This sort of behaviour is not the appropriate response to a planned public protest such as the long march," a statement said.
The British mission urged all sides to pursue political goals through democratic and peaceful means at "a critical time for Pakistan."
"Political opponents should work for reconciliation so that they can concentrate on the grave threats facing the country," it said.
Britain, the former colonial power on the sub-continent, and has retained a certain degree of political influence in Pakistan.