I did not expect to Shift Likely but it's as well
Last year I went though all the posts of Pegomya solennis.
Whilst I think there is a very good chance that you are right here, there is no supporting comment, nor even mention of the host plant.
And it is still only a chance, there being other 'blotch' miners in Rumex (which I assume this is)
I usually go through other posts of these (obscure) observations - there are never many in Other Observations. I feel compelled to offer comment and be generally supportive and encouraging whenever possible.
For my post last year I looked at every other one in iSpot - a useful exercise.
Now see http://www.ispotnature.org/node/817566 - consider the detail but yet, still only one agreement!
THREE MARINE PROJECTS
Lat/Lng: 52.0005, -0.71266666666667
OS grid ref: SP884343