Nah wasn't me, but I remember the tunnel was put in about '54 or '55. My parents used to take me to 'London Airport' by bus from our home in South Bucks during school holidays (Greenline [713?]from Chesham to Uxbridge then red LT bus, returning by green LT bus to Slough then the 353 back to Chesham). In the early days before the tunnel we got off the bus on the Bath Road and would walk across a taxiway to get to the public enclosure; later we walked though the tunnel (it was allowed in the early days but not now).
The tunnel was I believe constructed using the 'cut and cover' method rather than by boring; I think there was an airborne illustration in the 'Eagle Book of Aircraft' c1956.