This, alongside autumn, is the best time of year to get grass established, so I'd sow if I were you. Have you prepared the soil? Once you have, sow the seeds, give them a good soak and keep the bastard birds off.
Clearing the last of the weeds/ivy today. Soil seems great, to my uneducated eye. Will be scarifying/loosening with an asphalt rake, sowing, raking, pacing over and setting up the sprinkler.
This, alongside autumn, is the best time of year to get grass established, so I'd sow if I were you. Have you prepared the soil? Once you have, sow the seeds, give them a good soak and keep the bastard birds off.