o1 <- gIntersection(ud50_m2b,ud50_hmm,byid = T, id = 'ID')

Error in RGEOSBinTopoFunc(spgeom1, spgeom2, byid, id, drop_lower_td, unaryUnion_if_byid_false,  :   ids vector has incorrect length of 1 expected length of 35910

> str(ud50_m2b)
Formal class 'SpatialPolygonsDataFrame' [package "sp"] with 5 slots
  ..

@ data       :'data.frame': 2 obs. of  4 variables:
  .. ..$ ID    : Factor w/ 2 levels "CB1201","CB1203": 1 2
  .. ..$ area  : num [1:2] 1971 1178
  .. ..$ survey: Factor w/ 15 levels "","April2012BI",..: 2 2
  .. ..$ n     : int [1:2] 3024 4326
  ..

@ polygons   :List of 2
  .. ..$ :Formal class 'Polygons' [package "sp"] with 5 slots
  .. .. .. ..@ Polygons :List of 3
  .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
  .. .. .. .. .. .. ..@ labpt  : num [1:2] 435288 6250135
  .. .. .. .. .. .. ..@ area   : num 5857355
  .. .. .. .. .. .. ..@ hole   : logi FALSE
  .. .. .. .. .. .. ..@ ringDir: int 1
  .. .. .. .. .. .. ..@ coords : num [1:30, 1:2] 434056 433968 433882 433922 434056 ...
  .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
  .. .. .. .. .. .. ..@ labpt  : num [1:2] 442476 6251628
  .. .. .. .. .. .. ..@ area   : num 13697898
  .. .. .. .. .. .. ..@ hole   : logi FALSE
  .. .. .. .. .. .. ..@ ringDir: int 1
  .. .. .. .. .. .. ..@ coords : num [1:64, 1:2] 439588 439576 439588 439740 439983 ...
  .. .. .. .. ..$ :Formal class 'Polygon' [package "sp"] with 5 slots
  .. .. .. .. .. .. ..@ labpt  : num [1:2] 442305 6247942
  .. .. .. .. .. .. ..@ area   : num 156406
  .. .. .. .. .. .. ..@ hole   : logi FALSE
  .. .. .. .. .. .. ..@ ringDir: int 1
  .. .. .. .. .. .. ..@ coords : num [1:8, 1:2] 442353 442112 442185 442353 442474 ...
  .. .. .. ..@ plotOrder: int [1:3] 2 1 3
  .. .. .. ..@ labpt    : num [1:2] 442476 6251628
  .. .. .. ..@ ID       : chr "CB1201"
  .. .. .. ..@ area     : num 19711659