I have no problem transferring the copyright after payment (which is standard practice). However, I've never been asked to do an agreement like this before, and the implication seems to me that this is more about protecting themselves from copyright infringement. That is if someone decides what's been written is too close to something of theirs, I'm the one who gets sued.
Now, I'm not going to just copy and paste someone else's work. But I'm going to be relying on what the client supplies me and I don't know where they're getting it from. I'm also going to be relying on what another copywriter produces for a large chunk of the project. Copyright is also a grey area - just how much of someone else's information do you have to change for it to be considered your own?
Surely if I'm doing work direct for the end client, it's up to them to be satisfied with what they put on their website? (If it was via a third party like a web designer it might be different.)
I've certainly never been asked to sign an agreement like this before. I'd be interested to hear suggestions/experience from other UK copywriters, or indeed from those from other countries.