Testing with Opera Mobile Emulator

I have been using Opera Mobile Emulator to test a few of my websites that have Mobile Joomla installed. All were working as expected, and correctly used the mobile template. One of the sites used to work correctly but now - oddly - when I use Opera Mobile Emulator, it only displays the default template for the desktop. I tried un-installing and re-installing Mobile Joomla, but this did not correct the problem. The website is:

birminghambotanicalgardens.org.uk

Any ideas - help appreciated.

John