Caution ex-PM, cycling on motorway in front of Tesla (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

A charade of MI (i.e. M1, ‘motorway’) plus STRUS, which is TRUSS (Liz, ‘ex-PM’ If you blinked, you may have missed her) ‘cycling’ plus T (‘Tesla’, unit of magnetic flux density). “Treat any Special Offer on the internet with caution. If it seems too good to be true, it probably is”