It would be very easy to allow your head to swim up to the clouds and announce boldly that you are the best selling author of all time, even if this isn't quite true - yet! Perhaps the initial shyness has dilluted now that you're more used to the conversation with the newly discovered reader, but modesty should remain for all good British folk! It's part of our culture and whilst we tend to build in confidence we are a modest nation by default.
The tricky part of 'realization cycle' is to know when to advertise and talk freely and when to deploy the natural look of 'well of course, but hey, it's nothing. Thanks for noticing,' with a confident smile. There's a time and a place for advertisement and PR and for boasting one's own career with friendly chit chat. Book events and conventions are the places for these. You can go a little way along the path of 'here's the address of my website' conversation but if it's a casual enquiry born out of surprise , it pays not to overdo it. I did warn you, it's tricky, but the only golden rule I can work by myself is; 'just be yourself, always smile and be pleasant. Never be pushy.' We hate pushy people in the UK. Think about the car salesman who 'was lovely, never tried to push me into it,' and how often that person won the sale. The one who 'was all over me the minute I walked in the door,' will earn far less commission in life.
So - give it your best sweet smile and pray the enquiry is converted into a sale at some point down the line - but never push your luck! In short, keep your feet firmed on the ground, your head out of the clouds, and your eyes open to the world around you. We have two ears and one mouth... not a bad rule to remember. Good luck!