SVR Stalybridge - Gatwick route 'Via Manchester' is £62.35 is one option.
This is mapped
Stalybridge - Manchester - Chinley (map GM), Chinley - Sheffield - Grantham - Sleaford (map PS), Sleaford - Peterborough - London (map ER)
Also ok
Stalybridge - Manchester - Chinley (map GM), Chinley - Sheffield - Doncaster (map PS), Doncaster - Lincoln (via Retford or not via Retford) - Sleaford - Spalding - Peterborough - London ( Map ER)
Also ok
Stalybridge - Manchester - Chinley (map GM), Chinley - Sheffield - Doncaster (map PS), Doncaster - Grantham - Sleaford - Spalding - Peterborough - London ( Map ER)
Not OK as far as I can see is Stalybridge - Manchester - Sheffield - Nottingham - Newark - Lincoln - Sleaford - Spalding - Peterborough - London
A Manchester - Gatwick ticket would NOT work, as this ticket only valid via west coast line.
First valid train from Manchester is the 09:35 to Euston. Sunday unrestricted between Gatwick and Sandy,
Monday restricted from Sandy to Pbo only (not before 10:07, nor after 15:33)
Hence options:
Sandy to Pbo
10:07 arr 10:39 plat 2
Possible connection????
10:40 (plat 1) to Lincoln, calling Sleaford 11:25, Lincoln 12:01
then
SLR-NOT 12:12 arr. 13:22
NOT-MAN 13:47 arr 15:36
or
SLR-GRA 12:12 a 12:41
GRA-DON 12:49 a 13:24
DON-MAN 13:42 a 15:03
or
LCN-SHF 12:27 arr 13:48
SHF-MAN 14:11 arr 15:03
Otherwise
SDY-PBO
11:07 arr 11:39
from PBO
11:50 to Doncaster, calling Sleaford 12:38, Lincoln 13:14, Doncaster 14:07
either
SLR-NOT
13:13 arr 14:22
NOT-MAN
14:47 arr 16:36
or
LCN-SHF
13:26 arr. 14:48
SHF-MAN
15:11 arr 16:03
or
DON-MAN
14:42 arr 16:03
otherwise
SDY - Pbo
11:33 arr 12:06 p1
or
12:07 arr 12:39 p2
Connect Pbo
12:41 (plat 1) to Lincoln, calling Sleaford 13:26, Lincoln, 14:03
then
slr-not
14:13 a 15:23
15:47 a 17:35
or
slr-gra
14:13 a 14:41
gra-don
14:49 a 15:25
don-man
15:42 a 17:02
or
lcn-shf
14:25 a 15:48
shf-man
16:11 a 17:02
Then
Sandy - Pbo
12:33 arr 13:06 p2
or
13:06 arr 13:38 p2
connect
13:41 (plat 1) to Lincoln, calling Sleaford 14:26, Lincoln 15:03
SLR-NOT
NOT-MAN
15:12 a 16:22
16:47 a 18:36
or
LCN-SHF
SHF-MAN
15:25 a 16:48
17:11 a 18:03
Then
Sandy - Pbo
13:33 arr 14:06 p1
or
14:07 arr 14:39 p2
or
14:33 arr 15:06 p1a
15:11 (plat 1) to Lincoln, calling Sleaford 15:56, Lincoln 16:47
SLR-NOT
NOT-MAN
16:10 arr 17:22
17:47 arr 19:36
or
slr-gra
16:10 a 16:41
gra-don
16:49 a 17:24
don-man
17:42 a 19:03
or
LCN-SHF
SHF-MAN
17:22 a 18:34
then
18:40 (below minimum connection) a 19:36
or
19:11 a 20:02
Then Sandy - Pbo
15:07 arr 15:39 p2
or
15:33 arr 16:06 p1a
From Pbo
16:25 (plat 1b) to Lincoln, calling Sleaford 17:16, Lincoln 17:50
Then
SLR-NOT (this train avoids Grantham)
18:27 arr 19:22
NOT-MAN
19:47 arr 21:36
or
LCN-SHF
18:25 arr 19:53
SHF-MAN
20:11 arr 21:03
or
either Sleaford, Ruskington, Metheringham, or Lincoln (40 minute wait in each case) -DON 19:25
DON - MAN 19:42 arr 21:03