Recent hot and dry weather for many regions have provided good windows of opportunity for harvesting in the past two weeks, according to AHDB's latest report.
The GB winter barley and winter oilseed rape harvests are now finished, with winter wheat harvest 99% complete, the report, which covers the week ending 12 September, says.
Spring barley was 87% complete to the week ending 12 September, which is behind the previous five-year average of 92%, but a jump up from 59% complete in the previous report a fortnight ago.
Oat harvest was 98% complete to 12 September, ahead of the 5-year average of 91%, according to AHDB's harvest report.
Though progress can be seen for many over the past few weeks, there are reports of green crops in some regions still, particularly for spring oats.
Key regions with area still to be harvested are across the North East and Scotland.
Megan Hesketh, AHDB senior analyst explained more: "With the improved weather seen over recent weeks, less grain drying has been reported over this period in some regions.
"Straw yields have been variable across the regions and crop type, with late sown crops generally poor.
"A lot of straw has started to look weathered, although improved recent weather conditions provided good baling opportunities."
She added: "Quality remains in focus considering the wet weather we have seen through most of the summer.
"Typical Hagberg falling numbers are now ranging between 200–220 nationally, in data to 12 September, with some regional variation. This is down from 220–250 in the last report a fortnight ago."
Notably from the last report, the GB average yields for spring barley are lower, at 5.3–5.7 t/ha, slightly down from 5.5–5.9 t/ha.
"Grain yields have seen clear variation this season," Ms Hesketh said, "Overall, crops grown on heavier land have yielded better.
"Sowing date too has been particularly important for spring crops."