Hi FDOS_UK. I have also been turned away twice last year at MAN. First time seemed genuinely full but second time was because they had not cleared the tables from departing guests. Not surprising as I could see 2 staff in the kitchen typing on their smart phones and the woman on the desk was on the land line to a friend. I had to wait 3 minutes until she could tear herself temporarily away from her call, to refuse me access.
BHX is as bad as they “reserve” multiple tables for premium travellers on KLM / AF / LH who might turn up.
At both of those lounges, if you have an Aspire lounge access card they are not able to turn you away.