i had to look and see if England has morels and it looks like it does:
When it comes to foraging for morels, this fungi is deservedly one of the most highly regarded and prized and this is why we always get excited when Morel season comes around again each spring. They’re so expensive because it’s very difficult to cultivate them – Scientists have been trying…
totallywilduk.co.uk
[from the article]
"Morels typically appear in the spring, and tend to prefer sandy soils or recently laid woodchip."
i agree with these observations.
my guess is that clay is not going to be the best place for them. here they are growing in places that have some drainage and not at the bottom areas where any water might collect. you probably would need a slope of some kind and perhaps you would also need some sandy soil and perhaps mix it with some peat moss and then mulch over it with some crushed rinsed limestone and mix perhaps with some beach stones that are not as harsh as using all crushed rinsed limestone. the other thing i would suggest would be to put a heavy liner underneath it to prevent weeds, grasses and ants from coming through it - you don't want the clay to mix with your lighter topsoil.
here the conditions they've come up in are various but all of them are in the limestone mulched areas that have been aged for quite a few years. there has been sand and wind blown detritus and moisture from rains rinsing off the crushed rinsed limestone so it isn't as harsh as it would be if you were starting off at first and were putting down fresh mulch.
it's not going to be a sure thing as i think morels are pretty finicky about conditions but if you can get some areas that get some morning warmth from the sun and they are drained well enough they might eventually work out. the other thing needed after some weathering and settling in would be some morel mushroom spores and the best way to get those is to find someone who goes out collecting them and pay them for a few fresh ones that you can rinse off and then scatter that water on the areas you've prepped along with any other areas in your property that might work. don't worry if you don't get it right. the millions of spores will spread around and eventually some may find a workable spot to grow and eventually send up a fruiting body (aka the mushroom we like to see and eat

).
this might take years to actually work. i think that we were lucky in that we'd already had a lot of areas mulched and covered for years before i scattered the morel mushroom rinse water around. we'd previously not had any morels anyplace on our property, within a few years of scattering the rinse water around i saw the first morels popping up.