Boggy Lawn

Hi All, looking for some help with a very boggy lawn.

Last year I put in some french drains but this doesnt seem to have worked too well (not this winter anyway!) see pics. I also use a hollow tine aerator and fork the lawn regularly but to no avail...
Based in South Wales and the soil is Clay.

Im looking at putting a shallow S shaped block paving path in leading from the patio to the decking around Easter time, so I was going to dig down 3ft and fill with 20mm gravel in a membrane to use as a kind of large garden soak away.

I was wondering if i will need to dig the whole lawn up around it and do the same but with 2ft of gravel then a foot of topsoil then turf on top to stop the boggyness in the winter.

any other ideas welcome.