I will be installing 4m2 of solar panels linked to a triple coild 259 solar hot water tank. The bottom coil will be connected to solar, the middle one to the woodstove with backboiler and the top coil to a new oil condensing boiler. The connection of the solar panels and oil boiler with cylinder stat is fairly straight forward. I am not sure yet how to connect the wood boiler. There used to be an open vented woodfired system in the past so I can use the old tank that is now no longer connected to anything by reconnecting it to the mains and the piework just outside the boiler. The bottom of the cylinder will only be 20 cm over the top of the boiler and about three meters away, I will therefore need to use a pumped system to get the hot water to the cylinder from the 800 or 10000 btu boiler. If I use a thermostat to allow heated water to be re-directed to a towel radiator if the cylinder has reached the desired temperature do I also need to include an additional heat sink radiator in the loft to comply with building regulations. How likely is it that this tower radiator will ever get hot enough?

AND the system MUST be capable of gravity circulation.
Many modern Multicoiled cylinders need to be pumped and can otherwise airlock!
Why not use a direct connection to a thermal store .
The recommended minimum "gradient" for gravity is still one in three!

a thermosyphon will likely work for you.