Does anyone know if this includes gas bottles and/or battery? Pretty certain that the battery is not, the handbook says that gas cylinders are included. I have not been able to work out any definitive answer

MIRO is a bit of a moving target. Firstly it is the weight of just one, usually prototype van in order to register for type approval. Actual production vans often weigh more due to the tolerances in production materials and appliances.
MIRO regs don't stipulate an actual amount for either gas or water, just stipulating that there should be an allowance. Many UK makes include a 10kg gas allowance which is odd when a 6kg Calor cylinder weighs 14kg when full. To find out what's included in any particular MIRO for any particular year you need to check the brands spec sheet very carefully.
The other thing to be aware of is that Eriba Touring van MIROs are for a very basic spec. van and most have many cost options added, which use up payload. In addition a battery and mover is never included in MIRO, so adding them to a van uses around 55kg of payload. In the case of Eribas it's even more because the equipment to charge and control a battery has to be included as it's not standard. HTH

Many thanks for your reply. Our van registration plate actually lists the MRO as 100kgs, which I find hard to believe, and just adds to the confusion. The manual and a notice in the van also disagree! The dealer told us that the MRO is 720 and payload is 180. We have been deducting the weight of gas bottles, battery and mover from the payload since we bought it. Interestingly Leisure First now only state not laden and unladen weight .We have never had problems with towing the caravan but the new car we now have made me redo the calculations, not easy with the different figures quoted.

MTPLM is the maximum a van can weigh when loaded. The noseweight load cannot be removed as it's the total weight of the van is what counts. What it does mean is that when towing your van never puts it's full weight through the two road wheels. It's a silliness that should be more clearly defined by regulation, but isn't. I suspect the 100kg figure mentioned by the OP is the noseweight limit, aka as Axle 1 on VIN plates. VIN plates don't show MIRO's, only weight limits.