Here are the published MCTs for LHR:
Code:
LHR-LHR FROM - TO D/D D/I I/D I/I
CC FLTN-FLTR ORGN EQPTM-CC FLTN-FLTR DEST EQPTM HMM HMM HMM HMM
1- TN 130 130 130 130
2- TN 130 130 130 130
3- TN 130 130 130 130
4- TN 130 130 130 130
TN- 1 130 130 130 130
1- 1 045 045 045 045
2- 1 115 115 115 115
3- 1 115 115 115 115
4- 1 100 100 115 100
5- 1 200 200 200 200
TN- 2 130 130 130 130
1- 2 115 110 115 115
2- 2 --- --- --- 100
3- 2 --- 115 115 115
4- 2 130 130 130 130
5- 2 200 200 200 200
TN- 3 130 130 130 130
1- 3 115 115 115 115
2- 3 --- 115 115 115
3- 3 100 100 100 100
4- 3 130 130 130 130
5- 3 200 200 200 200
TN- 4 130 130 130 130
1- 4 130 100 100 100
2- 4 130 130 130 130
3- 4 130 130 130 130
4- 4 130 045 045 045
5- 4 200 200 200 200
1- 5 200 200 200 200
2- 5 200 200 200 200
3- 5 200 200 200 200
4- 5 200 200 200 200
2- 5 200 200 200 200
3- 5 200 200 200 200
4- 5 200 200 200 200
5- 5 100 100 100 100
IE 1- 4 --- --- 115 115
ACI 1- 4 --- --- 115 115
GCI 1- 4 --- --- 115 115
JER 1- 4 --- --- 115 115
However, with regards to the OP, since those are two seperate tickets on two spereate reservations, I strongly recommend not to cut it to close since BA will very likely charge a walk-up fare if the ticketed flight would be missed...