Anything is possible in theory - Just need to work out max demand, and pick the correct size cable. SWA (Steel Wired Armour) ain't cheap. However it is necessary in this situation.
8.5kW / 230V = 36.9A (Amps) so your cable needs to be rated for this as a minimum.
Generally Voltage drop is only a factor for runs over 100M Including the final part of the circuit. Generally (There is too much detail to go into).
6mm 3 core SWA will give you 46A 'to play with' you could cheap out on 2 core and use the sheath as earth. I'd rather not. Currently 100M reel of SWA 6mm is £253.00.
4mm is rated at 36A however there are de-rating factors to account for. 6mm is a safe bet.
You will need to assess the total load that is likely to be placed upon the circuit and then calculate the size of cable (Steel wire armoured) that is required. because of the distance you need to comply with the current regulations taking into account external influences and the voltage drop that will occur.
Richard @ Galvin Electrical