John Perryn

On the west wall of St Margaret's Church Westminster is an oval tablet to John Perryn who was buried in the church. It reads: 

To the memory of John Perryn Lieutenant Colonel of the 12th Regt. [Regiment] of Foot a man as eminent for his private virtues as for his professional abilities; who after serving his country for 36 years (a great part of which was spent in the active and hazardous duties of war in Germany, in Flanders, in Holland and in the glorious defence of Gibraltar against the united efforts of France and Spain) fell a victim to a malignant fever contracted in an expedition to the coast of France on the 23rd day of January 1796 in the 57th year of his age: and was buried in a vault beneath this church.

Further reading

His will is at The National Archives (there was also a Major John Perryn in the 12th regiment who died in 1805)