yep - sounds like classic ignition switch failure. Dash lights still on? Radio still paying? No loud 'clunk' when removing key?
Best to disconnect battery between uses until you get ignition switch fixed so as to not drain your new battery...
Part (from an Audi dealer) should only be ~ $35. Can be had online for $8.65 from
www.************************************************************ so weigh your options b/w express shipping from them vs local pick up.
EDIT - sorry, just saw you are in UK so above is reference to prices here in US