I have 2820n router that I need to be able to block all internet activity except for one site for a specific pc.

Now I have managed to block all internet access to this specific pc by creating a filter set to block all web traffic form the source ip to any destination ip.
I also created another rule to allow access to the BBC website by setting the destination ip as 212.58.246.94 and moved the rule above the block filter rule. By doing this I can ping the BBC site successfully & receive a reply but when I try & browse to the website I cannot connect.

Any ideas where I may be going wrong?

Cant you turn on the URL Content Filter and then allow the other machines through this filter using the excepting subnets/IP addresses - you could make sure all the other PC's are part of a particular subnet.....

It sounds like DNS is failing? Are you pinging the IP or the hostname? If you can ping the IP but not the hostname then open UDP port 53 to that PC and that should work I think

I am able to ping both host name & ip address, in actual fact it is allowing me access to the bbc website but extremely slow, taking at least 10 minutes to start loading the page & it dosent load fully making the site un browse able.

It seems im half way there i just need to further tweak the router in some way