Enterprise collaboration app maker Slack shrugged off concerns about the UK’s pending exit from the EU, by opening of a new office in London.

The move signals Slack’s backing of the UK, which CEO Stewart Butterfield told Bloomberg is its second largest market outside North America.

“Brexit or no Brexit, London is still London and the UK is still the UK,” Butterfield told the news agency, adding: “About half of our daily active users are outside North America.”

Butterfield said about 30 per cent of the company’s users are in Europe: “Eventually we’ll open offices on the continent as well just because we have customers in every country in Europe at this point,” he said. An office in mainland Europe is planned for later in 2017 or in 2018.

Slack wants London to be “a sales-led office,” and aims to increase the number of employees from five at present to about 20.

Overall, the firm has 800 employees in seven offices, including one in Dublin.

It follows in the footsteps of companies like Facebook which said it wants to increase its UK employees by 50 percent and hire 500 more pepople.

Snap also named London as its international hub while Google may add up to as many as 3,000 staff, the Bloomberg report said. US-headquartered VR app maker Jaunt in February also chose London as the spearhead of broader European expansion.

In April 2016, Slack raised $200 million and was valued at $3.8 billion. Since launch it raised a total of $540 million.

“We’re growing at a fair clip still and one of the things that’s a side effect of that rate of growth is that predictability is hard,” Butterfield said.

“The good news is that the private capital markets are very friendly to companies like ours right now so there’s no need for that public offering.”

As for an IPO, the CEO it was “years away.”

Meanwhile, Microsoft is reportedly working on Skype Team following a failed $8 billion bid for Slack and Facebook’s Workplace app is said to go head-to-head with Slack.