when does filtering become DWDC?

[maddog04]

I was told by a cop that there's no legal definition for filtering ref speed
it is legal to filter and its recognised in the Highway code
IMO filtering above 25mph on a motorway is foolish to say the least as stationary traffic still move out to change lanes/block you....observation is key, if you're filtering at 70+ between traffic (moving or not) then you're a twat who's asking for trouble