It was a hot and fairly slow-paced but steady day's digging in Forty Hall today, as we enter the second week of this year's dig, and temperatures are gradually climbing towards dangerously record-breaking highs.

Thankfully today the weather was bearable enough under the cover of the lime tree avenue for digging to continue and for members of the public on our well-attended second open day to enjoy the family activities, guided tours and talks by the site director on what we've been up to this week.

Unfortunately the contents of this year's trenches are not as photogenic as they have been in recent years, and the best we've been able to offer visitors to the site are views of the ubiquitous rubble rich deposit filling the cut of what we think may be the moat that separated the outer and inner courtyards of the palace.

In trench 1 we have now established a clear and almost vertical cut line defining the eastern side of the 'moat'. This cut is so steep we are again rapidly reaching the safe limit of depth and will probably not be able to see the base of the feature in this trench.

Meanwhile in trench 3, the rubble context continued to be removed but it is looking very unlikely that the trench will find the hoped for rising western edge of the cut, which would have gone a long way to confirming the moat theory.

A similar story is unfolding in trench 2, where we are struggling to accurately define the cut line, due both to its highly irregular shape and the fact that the rubble-rich deposit is mixed at its base with lenses of redeposited natural brickearth.

Our diggers' hard work was well rewarded, however, with a rich assortment of varied finds including copper alloy pins, more delicate aglets, window glass and a variety of pottery, and the first star find of the day from the fill of the sloping cut in trench 1 - a large and almost complete iron key.

The key is only missing one of its two 'bits' (perhaps the reason it was discarded?) and although oxidation and concretion have added to its size, it must once have opened a quite substantial lock for a fairly hefty door or gate.

We have quite a lot of contemporary accounts that mention the palace's locks - under Henry VIII this work was often carried out by Henry Romans, the king's smith. New locks were typically installed just before a royal visit and removed when the court departed - but this is first ever archaeological evidence of that work.

Since we are on a hunt for the inner gatehouse, it is more than tempting to imagine this key opening the very gate we've been looking for.

The key was almost upstaged late in the day though, by a fantastic and very rare find in trench 2, in the form of a decorated glazed 'Penn' floor tile.

Penn tiles, named after the Buckinghamshire town in which they were made, are a distinctive often elaborately decorated red and yellow glazed patterned tile which adorned the floors of many higher status buildings in the middle ages.

They are closely dateable to the 14th century and often featured tessellating geometric and floral patterns, as well as animals.

This example has one intact (probably upper-left) corner, part of a zig-zag cog roundel and what we think is probably the figure of a hare or rabbit, most likely part of a hunting scene.

Evidence from this period in the palace's history, before its expansion into a grand brick-built mansion by the Earl of Worcester in the mid 15th century, is vanishingly rare, and although this tile was not in situ its underside did still bear a considerable amount of mortar, which may be a sign that it hasn't travelled far from the floor it once adorned.

Owing to the Met Office having issued a red weather warning for tomorrow and Tuesday we won't be back in Forty Hall now until Wednesday when hopefully things will have cooled down enough for us to finish at least partially unravelling the puzzle of the gatehouse and its moat before we begin backfilling at the weekend.