Regardless of who was at fault I think the question anyone involved in an incident like this needs to ask themselves is 'could I have done something to prevent it happening?' I prefer to filter up the outside of traffic where possible, but that road doesn't lend itself to doing that (I know the road well). So, I'd suggest there are 2 ways you could have avoided being knocked off:
1 - Not filtering at all.
2 - Filtering very very carefully, especially when there is a chance that a vehicle will be turning left into a side road or other entrance.
Personally, I take the second option. I'd go as far as to say it's probably best not to undertake at all if there is a side road / entrance on the left.
Please don't misinterpret my comments as suggesting that you're at fault. BUT, in an incident like that there's only ever going to be one injured party and I think it makes sense to ask what / how / if you could grave avoided it.
Edit - what bought this thread to my attention was doing a search for 'Nottingham' to see if there were any posts about the cyclist who died this morning on Crown Island (which is about 2 miles from where the OP's incident was
).