The British Library released an iPad app a couple months back, and yesterday that app was updated. I wouldn't get the update if I were you; it locks the content behind a paywall. I'm limited now to only 100 free titles now (down from 1k before).
The good news is that the ebook collection has been expanded. The app now has access to 45 thousand scanned books from the 18th and 19th centuries, and the collection should expand to over 60k by the end of the year.
You can only access the collection if you pay a $3 a month subscription. I don't see a need to pay; I have plenty of old books to read elsewhere.