It's not that uncommon. Last year we were below 100g/kWh (the 2030 target) for about 20% of the time. We averaged 83g today.

Chart from mygridgb.co.uk

Look over the last 12 months and you'll see renewables are 30% over the year. 30% Gas, 15% Nuclear and 10% Biomass. The rest is imported from France (mostly Nuclear) and Norway (Hydro).

This year should see another 3GW of wind start up at Dogger Bank, with similar amount scheduled for the next couple of years. This will be more and more common.