Nintendo did not reveal an exact price for the Nintendo Switch for UK customers during the conference for some unknown reason, but after the conference had finished, Nintendo UK revealed the price on Twitter. The price will be £279.99 at launch according to Nintendo UK.
Here is their tweet.
#NintendoSwitch arrives on March 3rd 2017 and will be £279.99 on the Nintendo Official UK Store.
► https://t.co/MGP8K1wgl2 pic.twitter.com/WlYig3ni0O
— Nintendo UK (@NintendoUK) January 13, 2017