Leeman (Dutch and English)and Lehmann (German) are pronounced the same. One family of my close relatives spell their name Leemon. The reason is that clerks and informants were either not all that literate or didn't bother too much about precise spelling. Our name appears in the parish records as Leman, Lemon, Leeman, Leaman and even Lennon.
Many of the Dutch and German Leeman/Lehmann family have an ancient Jewish origin dating back to the first century AD when Jewish slaves were taken to the Rhineland frontier by a Roman Legion that had suppressed the 70AD Jerusalem rising. These Leemans were from the Tribe of Levi - priests.The Germans say that Lehamnn means Levite or lender.The first interpretation may come from the Aramaic Al Iman/Imam (priest).The oldest inscription in the world referring to Hebrews (700 BC in Tigre on the Ethiopian plateau) says that their Sheban king was LMN.
Many Leeman/Leemons in Ulster take their name from the Scots Lamont clan.
The Dutch/Jewish name Leeman in Ireland may come from two German/Alsace brothers who arrived there via Scotland in the 17th century (the channel was closed because of the French wars). They were not Jews but converts to Christianity.Nevertheless they seem to have intermarried with similar families (the Poolers)and kept their origin a secret until 1916 when the Goldring family in Belfast raised the issue.I still get hate mail from one family member for discovering this.
The other area of Britain where the Leeman name is common is around York and Hull where there was a large Dutch settlement to clear the Fenland. Leeman Street is a main road in York and George Leeman was a famous MP there.
Leeman is also a common name in Belgium among the Flemish. Informants in Amsterdam tell me Leeman is a common Dutch Jewish name of Ashkenazim origin (West European rather than Spanish-Moroccan).