Buying a suitable UK flexwing
As the current wing appears very similar to the venerable Pegasus "XL", and is presumably a pretty docile, slow flying example, you are going to have problems finding a Section "S" approved equivalent. No current UK built flexwing would be comparable (speed being the thing these days), and all the existing XL's are getting very long in the tooth. One of the French UK legal trikes has a similar wing, but I don't think there are many of them about.
You might spend more time and money trying to make a combination than getting the current machine past Section "S". There's more to it than just bolting an alternative wing on. The position of the wing base tube relative to the trike and pilot is important - having flown a Pegasus "Flash 2" for nearly 20 years, I'm familiar with the very different handling this can lead to. I think the single main flying wires need doubling up, which shouldn't be that difficult, but otherwise the rest looks OK. It would be worth seeing if Polaris could be persuaded to supply some stress calculations.
I don't think you would have a hope in hell of getting it down to SSDR weights - the Rotax 582 is a hefty lump, and this one appears to have a battery for electric start. The fuel tank also looks substantial. All the SSDR trikes are of very minimal construction, and many only have simple single cylinder engines.
TFP