Should expert witnesses be immune from suit?

I don't think so - they do their work for reward and if they fail in their duties of reasonable care (primarily to the Court and secondarily to their instructing party (ies)) then they should pay for the consequences accordingly.  Any fear which might put them off coming forward is countered by the fear which makes sure they do their best and comply with their duties.  There was an interesting discussion of this when the Court of Appeal ruled that expert witnesses have no immunity from disciplinary action  - see General Medical Council and Professor Sir Roy Meadow - the Supreme Court are set to answer the immunity from civil suit point on Wednesday (Jones v Kaney)....what this space...