London has two charges: Congestion Charge (£18/day in the centre) and ULEZ (£12.50 for non-compliant vehicles). Both are paid online.

If your international card doesn't charge foreign fees, tap it directly on the Tube and buses — it gets the same daily fare cap as Oyster. An Oyster card is really only worth it if your card charges fees abroad.
They're two separate charges run by Transport for London: the Congestion Charge applies in the centre on weekdays, while ULEZ covers nearly all of Greater London every day for the most polluting vehicles. Both are paid online at tfl.gov.uk.
They must run a meter, hold a TfL licence, and can be hailed in the street when the 'For Hire' light is lit. Uber, Bolt and minicabs must instead be pre-booked — hailing an unbooked car in the street isn't legal.
Call the free NHS 111 line, available 24/7: it directs you to A&E, a doctor or a pharmacy based on your symptoms. For a real emergency the number is 999 (or 112).
No. Check the restaurant bill first: a service charge of around 12.5% is often already included. If it isn't, 10-12% is standard; in pubs where you order at the bar, tipping isn't expected.
Major stations (King's Cross, Paddington, Victoria, Euston) have left-luggage counters with airport-style security checks. In high season, booking online ahead is worthwhile.
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