eMarketer latest forecast reveals that Google and Facebook will net a combined 68.5% of the £14.56 billion ($19.41 billion) UK digital ad market this year. eMarketer says the share will surpass 70% by 2021.

“Despite economic uncertainty due to Brexit, Google’s and Facebook’s ad revenues continue to grow at the expense of smaller players,” eMarketer forecasting director Shelleen Shum said. “When budgets are tight, advertisers tend to favor tried-and-true platforms that, on average, provide better measurement statistics and assurances against fraud.”

According to eMarketer, the lion’s share (83.4%) of Google’s revenues come from its search business. Google’s search will grow about 10% this year, capturing a staggering 79.9% of the UK search ad market.

Facebook’s net digital ad revenues will grow 25.6% this year to reach £3.77 billion ($5.03 billion). Facebook commands an 86.7% share of social network ad spending in the UK, far higher than that of any competitor. Twitter has a 4.7% share, and Snapchat follows with 2.8%. Facebook ad revenues are derived entirely from display advertising. This year, it will capture 58.5% of UK display ad spending, reaching 60.5% next year.