Step forward new tv architectural star . . . Isabel Allen. Co-author of The Bluffer's Guide to Architecture, this fresh new face came to prominence when the British Library was completed - and she was able to reveal to startled bbc viewers that she had been working on the project for many years, in fact before she was even born. 'Bluffing on the aj can be difficult,' murmured Allen in an unguarded moment this week. 'Bluffing on television is a real pushover.'