when does filtering become DWDC?

[Dead Eye]

It'll be really down to the interpretation of the copper who stops you.

That said, Met Police at a Bike Safe day suggest: a max 10mph difference to adjacent traffic and no filtering over 40mph. Which TBH seems fairly reasonable.

This is pretty much exactly what I do and feel comfortable with though I rarely filter anyway as most of my rides are luxury and not commuting therefore the situation rarely presents itself.

I will admit to some undertaking on the motorway though, but now that I think about it that has only ever been on the M25... lanes 1 + 2 seem to move much more freely for a motorcycle if you do undertake. I'd like to point out that I'm not zipping past at 3-digit figures here, just making progress at around 70, sometimes up to 80 to get past without lingering in a blind spot.