M271 has a roundabout in the middle, at the M27 junction (M27 goes underneath). M58 arguably has two, but that depends how you treat both the interchange with the M6, and the short single carriageway link to the A577. M4 Heathrow spur (especially if it got its own number, per original plans) would also count. For completeness, A601(M) and A627(M) have roundabouts in the middle of them. As does the M60 where it TOTSOs. Arguably the M12 in Northern Ireland (though arguable as whether that counts as British, and also if it's a terminal).
But as I said, most roundabout under motorway restrictions are at the ends of motorways (M32, M49, M50, M180, A8(M), A308(M)/A404(M), and spurs of the M3, M23 and M25), or at 4+-way motorway-motorway intersections that have 3 levels (M1/M62, M60/M62/M66, M8/M73/A8(M), M6/M61, M18/A1(M)).
The French A660 is, I believe, the worst offender (though none of the roundabouts are part of it - the autoroute ends just before each one, then restarts!) in the browser as tier-1.
But this is all a tangent...