Ian,
1. eCart does support the £ sign as standard this site uses as basic a eCart set up as you can get with the £ sign without any issues.
2. eCart in itself does not require PCI compliance it is the system you integrate it into that needs to be compliant if that makes sense. Basically if you do not store cc info (YOU SHOULDN"T EVER) and you use a secure checkout page and payment service provider with proper security implemented on your network you are nearly there. I am approaching this from a small business point of view larger companies will have slightly different requirements.