[html5] failure to validate mail link?

[designer]

Sorry if this is obvious, but a page I'm working on won't validate because 
of the mail link.

The validation error message is:

 Bad value mailto:designer at gwelanmor-internet.co.uk?subject=problem with 
RSPCA site
for attribute href on element a: WHITESPACE in QUERY.

the cut and pasted code is as follows:

<dd>N.B. If you have found a link which doesn't work, do please
        <a href="mailto:designer at gwelanmor-internet.co.uk?subject=problem 
with RSPCA site">TELL US</a>
        us about it</dd>

What am I doing wrong here? I've googled, but to no avail.

Thanks,

Bob