Wads of British Pound Sterling banknotes are stacked in piles at the GSA Austria (Money Service Austria) company's headquarters in Vienna July 22, 2013. REUTERS/Leonhard Foeger/File Photo

LONDON (Reuters) - Sterling hit the day’s high on Wednesday in volatile trade while shares in British companies slipped after British Prime Minister Theresa May and European Council President Donald Tusk said Britain had formally triggered its divorce from the EU.

May’s letter to Tusk, which she quoted from to parliament on Wednesday, said Britain and the EU must work together to minimize disruption and provide as much certainty as possible, and that a deep, special partnership was in the best interests of both sides.

Having earlier hit an eight-day low of $1.2377 GBP=D3, sterling jumped to $1.2478 after it was confirmed that the letter had been sent, up from around $1.2448 beforehand and leaving the currency up 0.2 percent on the day.

“I think this is largely attributed to reducing one element of uncertainty in the process of actually triggering Article 50 but also the conciliatory tone in Prime Minister May’s statement...focusing on the partnership with the EU and achieving a mutually beneficial relationship,” said Alexandra Russell-Oliver, a currency analyst at Caxton FX.

Sterling also hit day's highs against the euro EURGBP=D3.

Britain's FTSE 100 .FTSE index - most of whose earnings are denominated in other currencies - hit a session low after May triggered Article 50, down 0.3 percent.

British mid-caps also fell, down 0.1 percent.

British government bond futures FLGcv1 drifted higher, tracking German Bunds FGBLc1, to touch a session high around 20 ticks up from Tuesday's close.