Turns out it's a "Tree"
/It was a beautiful day today, so we spent some time in the garden working on the laptops near to our pots. We had lots of bees getting busy on the Lavender and Hebe. We saw some very small bees with bright yellow stripes and a reddy coloured bottom.
We checked the identification guide and they turned out to be the Early Bumblebee (Bombus Pratorum) - the first we have seen! We saw some too with the missing mid-band, just as described in the guide.
We also came to the conclusion the other smaller bees we had been seeing the with ginger "lifejackets" (as BCW calls them) were actually more likely the Tree Bumblebee (Bombus Hypnorum) rather than the Common Carder we thought they were (Bombus Pascuorum). The difference is mainly in the abdomen - the Carder has more of a ginger covering, whereas the Tree Bumblebee has a black abdomen. We'll try to get some photos over the next few days in order to confirm for definite.
The Tree Bumblebee is a recent addition to this country, so it's lovely to see them in our garden enjoying the plants so much!