It's not a house-fly (see tarsomeres)
No interactions present.
I'll agree with Graphomya maculata as an ID for this fly - It is a fairly distinctive species with its chequred black and white appearance as it feeds on umbels in mid-summer. One thing about this species is that it is sexually dimorphic, males and females look different. This is a female with the grey and white pattern - males have the white replaced with a bronzy-orange colour which makes one think they are a different species altogether.
Tachinid Recording Scheme
TRS Facebook Page
Thanks for the comments I had a look on-line and found this site
It's a better pic than mine and also shows the male
Lat/Lng: 52.2, -3.4
OS grid ref: SO0560