UK shares to buy: 2 high-growth stocks I’d snap up today While I own a number of large-cap British stocks, I believe small- and mid-cap stocks are generally the best UK shares to buy. History shows that shares in these areas of the market tend to outperform the large-cap stocks.Here, I’m going to highlight two UK mid-cap stocks I’d buy for my own portfolio today. Both have generated strong returns for investors in recent years, and I think they will continue to reward investors in the long run.5G is here – and shares of this ‘sleeping giant’ could be a great way for you to potentially profit!According to one leading industry firm, the 5G boom could create a global industry worth US$12.3 TRILLION out of thin air…And if you click here we’ll show you something that could be key to unlocking 5G’s full potential…5-year revenue growth of 540%The first stock I want to highlight is Keywords Studios (LSE: KWS). It’s a leading provider of technical services to the video gaming industry. It serves nearly all of the major players in gaming including Electronic Arts, Activision Blizzard and Microsoft.The reason I’m bullish here is that the video gaming industry is booming right now. Believe it or not, gaming now brings in more revenue than the movie and music industries combined. Looking ahead, this industry is only going to get bigger. Experts believe that by 2027, the industry will be worth around $300bn, up from around $150bn last year. KWS should benefit from this industry growth.Keywords has grown at an incredible pace over the last five years (revenue growth of 540%) and an update earlier this week showed the company still has plenty of momentum. The group said it has made a “very good start to the year” with total revenue growth of 36% for the first four months of 2021.There are a few risks to the investment case here. One is in relation to management. This week, the company announced CEO Andrew Day would be stepping down with immediate effect due to health reasons. This adds some uncertainty.Another is the high valuation. Currently, the stock has a forward-looking P/E ratio of about 38. That doesn’t leave a huge margin of safety. If growth stalls, the stock could take a hit.Overall, I’m very bullish on KWS however. It’s worth noting that yesterday, Jefferies raised its target price to 3,450p from 3,382p – that’s about 40% higher than the current share price.A UK stock for the digital worldAnother UK growth stock I’d buy today is GB Group (LSE: GBG). It’s a leading provider of identity management and fraud prevention solutions. Some of the world’s best-known businesses, including the likes of HSBC, Betfair, and Vodafone, rely on the company to provide digital identification services and keep business ticking along.Like Keywords, GB operates in a high-growth industry. According to MarketsandMarkets, the identity verification market is expected to grow from $7.6bn in 2020 to $15.8bn by 2025. That represents an annualised growth rate of 15.6%. Growth is set to be driven by more digitalisation initiatives and combating an increase in fraudulent activities and identity theft.GB published its full-year results for the year ended 31 March earlier this week and the numbers were impressive. Organic revenue was up 12.1% while profit before tax was up 66%. The group also said it’s made a good start to this financial year.This is another stock that’s quite expensive. Currently, it trades on a forward-looking P/E of around 44. That’s high by UK standards and adds some risk to the investment case. That said, I don’t think it’s that unreasonable, considering the valuations of US tech stocks at present. Image source: Getty Images. Click here to claim your copy now — and we’ll tell you the name of this Top US Share… free of charge! “This Stock Could Be Like Buying Amazon in 1997” Edward Sheldon owns shares in Keywords Studios, GB Group, and Microsoft. Teresa Kersten, an employee of LinkedIn, a Microsoft subsidiary, is a member of The Motley Fool’s board of directors. The Motley Fool UK owns shares of and has recommended Activision Blizzard and Microsoft. The Motley Fool UK has recommended Electronic Arts, HSBC Holdings, and Keywords Studios. Views expressed on the companies mentioned in this article are those of the writer and therefore may differ from the official recommendations we make in our subscription services such as Share Advisor, Hidden Winners and Pro. Here at The Motley Fool we believe that considering a diverse range of insights makes us better investors. I would like to receive emails from you about product information and offers from The Fool and its business partners. Each of these emails will provide a link to unsubscribe from future emails. More information about how The Fool collects, stores, and handles personal data is available in its Privacy Statement. Renowned stock-picker Mark Rogers and his analyst team at The Motley Fool UK have named 6 shares that they believe UK investors should consider buying NOW.So if you’re looking for more stock ideas to try and best position your portfolio today, then it might be a good day for you. Because we’re offering a full 33% off your first year of membership to our flagship share-tipping service, backed by our ‘no quibbles’ 30-day subscription fee refund guarantee. Our 6 ‘Best Buys Now’ Shares See all posts by Edward Sheldon, CFA Edward Sheldon, CFA | Friday, 18th June, 2021 | More on: GBG KWS Enter Your Email Address I’m sure you’ll agree that’s quite the statement from Motley Fool Co-Founder Tom Gardner.But since our US analyst team first recommended shares in this unique tech stock back in 2016, the value has soared.What’s more, we firmly believe there’s still plenty of upside in its future. In fact, even throughout the current coronavirus crisis, its performance has been beating Wall St expectations.And right now, we’re giving you a chance to discover exactly what has got our analysts all fired up about this niche industry phenomenon, in our FREE special report, A Top US Share From The Motley Fool. Simply click below to discover how you can take advantage of this.