Staring problem - Can anyone help or had the same

Morning all. I have had starting problem with my 200- free. About 3 weeks ago tried to start it at home, engine turns over but no spark! soon the battery is flat. I call my usual 4x4 garage (based at Puriton, Somerset - No name no pack drill) and he has to recover it to the work shops. Later that day after several phone calls, he has replaced the HT leads and distributer cap, boosted the flat battery and after £188 I'm back on the road. Today whilst visiting a site for work same thing, engine turns over twice without fireing then battery is flat - so flat that the hazards wont work or the back door open. Called AA, they boost battery and test. No reason can be found for loss of battery power - battery tests OK - alternator OK - I was advised by the AA man not to change the battery. I have driven through some water but no more than 6in and not fast as it comes up over the bonnet if you go to quick