The company, which launched at the beginning of March scored a clutch of customers during the Cheltenham Festival and is now preparing for the launch of its latest online offering - 21Bet Casino.
The casino site, which will be based on the same FSB sports betting technology as the 21Bet site, will feature games from the MicroGaming and Realistic Games stables.
Run by a team of sports fans and betting industry professionals, the team have launched a "Pick Your Promo" feature, which gives users a chance to submit their own ideas for betting offers and promotions.
"We said when we launched that we saw a clear opportunity for a no-nonsense betting proposition in the UK and our first month figures really bear this out," 21Bet chief executive Richard Hogg said.
"Everything about the site, from the design to the bets on offer, is about simplicity and fun. We do have special offers, sports news and insight, but the core of the site is all about good, old-fashioned betting. It's all about delivering a product that works for everyone from seasoned punters to curious first-timers. There's a lot more to come, but so far we feel we've made a pretty good start."
21Bet's purely online offering is likely to stand it in good stead in the current betting market. A recent report from Moody's said that despite the pressure from increasing taxes and regulation, online gaming markets are the most likely source of growth for gambling firms over the next few years.
Online gaming markets, according to Moody's, are expected to grow to approximately €42.8bn by 2018, up from €36.9bn in 2014.
Donatella Maso, a Moody's vice present and senior analyst, said: "Gaming companies with a larger online presence like William Hill and pure online company Sky Bet are likely to see higher revenue and earnings before interest, taxes, depreciation and amortisation (Ebitda) growth over the next 12-18 months than those more focused on traditional land-based business. This is a result of the continuing gradual shift online, mobile phone and tablet penetration rising, and fast-growing demand for online games increasing."