Stage Lighting And Effects Equipment

She lives in the country, just moved, in N.Devon (UK) and has been seeing 'fairy lights' at the bottom of her garden - seriously. I think this is probably Fireflies, but these colours are blue, and information I've looked up says yellow, green or red, but not blue. I'd be interested for any suggestions as to what this might be.

The surroundings are open fields, but no water apart from the river which is about 4 miles away.

Not sure about this category, but this is what's come up, so it's a start.
Not neighbours
Not the police (we don't see many around these days in the UK especially in the countryside!!)
I don't think she's about to go stumbling around out there LOL
But thanks all for your input.