Legally, no. But to protect yourself, yes. You need all kinds of liability insurance in case you have an 'incident' and someone brings a multi-million dollar lawsuit against you. But your real problem will be in the UK where is it virtually impossible to secure legally compusory car insurance for your US guests at anything approaching a reasonable rate. Try: www.aplan.co.uk/maidenhead/ But expect to pay maybe £300 for a month's insurance.