pancake filter won't fit. Why?

[nomis36]

Every time we do a job on my lads '91 mini it leads to another job, all part of the 'fun' though. Anyway, we fitted a minispares full exhaust system and intake manifold which went well. Unfortunately the intake didn't come with a take off for the servo so I had to get one off eBay, the only one I could find was straight. This now means the standard air filter doesn't fit as it fouls the servo pipe. No problem I thought, gives us the excuse to put a pancake filter on it. Bought one off eBay which is the same shape and size as the hundreds that are on there but for some reason won't fit. It's fouling the bulkhead at the bottom. We must be doing something wrong but don't know what. Do we need to remove the spacer between the carb and manifold?