if one has a self contained one bedroom flat, but have to share a bathroom, does that attract the bedsit rate or one bed self contain rate of LHA?

I think you have to have your own toilet and bathroom to be considered self contained . This link might help https://lha-direct.therentservice.gov.uk/Secure/pdfs/TRSHB(LHA)2OT.pdf

Single person under 25 would only get the shared room rate regardless of what they actually rent, unless they are a care leaver under 22 or would qualify for an SDP on means tested benefits, in which case they would get the self contained one bedroom rate.

For single people over 25 or couples the LHA guidance is
2.50 Single claimants aged 25 years and over and couples with no dependent children, will be entitled to the rate for a one-bedroom property, eg a one-bedroom flat or studio or other kind of self-contained accommodation, provided they actually rent a property of at
least this size (see note at 2.52).
2.51 However, if people in this category choose to live in a property where they do not have either exclusive use of two or more rooms, or exclusive use of one room, a bathroom and toilet and a kitchen or facilities for cooking, they will be entitled to only the shared LHA
rate.

Hence to get the self contained one bedroom rate your client would need his own bathroom and toilet and kitchen.

A working link to the document highlighted by traceyanne - Working out your Local Housing Allowance if you aged 25 or over and single -
can be found here -

https://lha-direct.therentservice.gov.uk/Secure/Default.aspx

...like buses, no replies and three come along all at once - thanks for them anyway - I suspected that might be the case......