Yes, it is banned. I saw signs on my recent trip to Wales. The roadworks between J12 and J13 to bring the dual carriageway there up to standard resulted in these yellow signs going up banning cyclists from J11 to J15. Can't quite make it out, but here it is underneath the brown sign: https://www.mapillary.com/app/?lat=53.2013595&lng=-4.11394&z=17&pKey=422956639351622&focus=photo&x=0.2679870765487419&y=0.45754226762179084&zoom=0.9582839116289317