Getting an extra Calor Gas cylinder

When I got my first caravan five years ago, it was second user, and amongst the other bits and pieces included in the sale, was a Calor gas butane 4.5kg cylinder, so since then I only had to pay the refill price when the cylinder has been empty.  A couple of years ago I decided I would like to have a second cylinder in my current caravan's gas locker- and was advised if I went to a Calor gas dealer I would have to pay an initial charge. My first thought was the local authority recycling depot- they have an area for leaving unwanted cylinders- but was firmly told that on health and safety grounds they did not sell empty cylinders to people!  Well, when I stayed at Hawthorn Farm CC site, I went into nearby Sutton on Sea, and they had a secondhand/junk shop which reminded me of Auntie Wainwright's in 'Last of the Summer Wine'. I had an enjoyable browse through the crowded rooms of junk- and saw a very elderly looking Calor Gas cylinder, very much worse for wear! I bought it for £5, went down the street to the hardware shop which advertised Calor refills, and asked them if they would take it so I could have a refill- no problem!