Hi thanks for your question. My name is Tony.
Can you tell me a little more about this please so I can tailor my answer accordingly?
we are involved in a property bid, at the third stage we made an offer of 'best offer plus £55k' amongst 12 bidders, the owners said that the bid is not valid
Okay. This will depend on the auctions terms, but it usually has to be a very clear offer and one which is capable of acceptance (i.e. best offer plus 55 might be considered uncertain) and one which is designed to allow you to fairly compete with others. I doubt, therefore, that the auction would recognise this as legitimate bid.
The bidding is being run by the owner with no terms stated other than best price, on a certain date