Cannot get chosen BDC to authenticate

I have a master domain with all the BDCS for about 10 different sites in. Its a NT network and we use WINS but it seems to be a lottery as to which BDC authenticates the user. The BDCs themselves are physically located on the user’s site (ie Leicester’s BDC is in Leicester) but there seems to be no way of forcing to use that. We have tried LMHOSTS file, SetLogonServer, static entries in WINS database, but the only thing that seems to work so far is disable the NETLOGON service on every other server until the one required logs the users in. Any help would be great thks. Clients are NT, Routers between sites,