There really isn’t much in the UK to compete with the breadth of the Ariel Nomad’s abilities. Certainly not for similar money, at any rate.
A Bowler EXR S, the street-legal descendant of the Wildcat, will keep you drier, propel you along much faster and deliver its own thrilling brand of off-road experience, but you can expect to lay out four or five times the Ariel’s cost.
Alternatively, for about the same sort of money, you can buy something like a Rage buggy in road-legal 200bhp spec. However, as sophisticated as these machines have become, they tend to remain on the heavily uprated quadricycle end of the scale, typically sporting bike engines and sequential gearboxes. Huge fun on the loose, then; probably less enjoyable to get back home again.
It should also be noted that the Nomad’s spec can be pushed in very different directions, resulting in a different sort of car on the driveway. There's masses of choice here and we won't try to sway you in any particular direction, except to say that the hydraulic handbrake was the most fun that any tester had while simultaneously clothed and covered in mud.
Depending on your preference, you can have the Ohlins dampers and a hydraulic handbrake with the intention of never leaving a grassy field – or you could ask Ariel to build you a supercharged Nomad with paddle shifters and spend your Sundays bothering Porsche 911 owners at Silverstone.