Based on this morning you should be OK with shorts & a t-shirt (or similar), but you may want to bring a light fleece just in case the wind picks up this afternoon.
T-shirt and a fairly thick shirt worn as a jacket did the trick. It was warmer than the forecast temperature.
Haddock and chips consumed, kippers bought and a "noon tart" to sample.
Picked up some Adnams beers.
Saw a Spitfire flying along the coastline and turning inland just north of Aldeburgh.
And, minutes after I'd commented about the lack of swifts in London this year, one repeatedly flew at me before veering off at the last moment and then hovering. It took me a little while before I realised that its nest was in the rafters just behind me.