Help with a simple implementation of hook_node_access_records and hook_node_grants

Using drupal 7 I have implemented hook_node_access but am having real troulbe figuring out how to go a step further and achieve the following using hook_node_access_records and hook_node_grants:

For a given content type ('submission') I want to limit users with a particular role ('curator') to see only node that have a specific value set ('location')

An abridged version of my hook_node_access function is outlined below.

Any help greatly appreciated.

Danny.

function hook_node_access($node, $op, $account) {

// Get the currently logged in users role
$role = is_string($account) ? $account : $account->roles[4];

// Get the node type being rendered
$type = is_string($node) ? $node : $node->type;


if (($role == 'curator') && ($type == 'submission')){

    $venue = 'london' 
    $location = 'london' 

    if (in_array($type, node_permissions_get_configured_types())) {
        if (($op == 'view') && ($venue !== $location)) {
            return NODE_ACCESS_DENY;
        }
    }

}

}