Quick information, hopefully in a nutshell...

I gathered these bits and bobs so that you no longer mix them up

Notes:

Class 357 - C2C Rail / Overhead wires / Square windows

Tightlock couplers, round gangway-less fronts 

357/0 - 4 coaches, 3+2 seating

357/2 - 4 coaches, 3+2 seating, 11 out of 28 remaining

357/3 - 4 coaches, 2+2 seating w/ grab handles (Metro), converted from 357/2 (17 of 28)

Class 375 - Southeastern / Third rail / Square windows

375/3 - 3 coaches, old lights, 311-328 transferred to SN and renumbered as 377/3

375/6 - 4 coaches, dual voltage, old lights

375/7 - 4 coaches, old lights

375/8 - 4 coaches

375/9 - 4 coaches, 3+2 except for cab ends

Class 376 - Southeastern / Third rail / Metro

376/0 - 5 coaches

Sliding pocket doors with doorway standees

2+2 seatings w/ tip-up seats near cabs

Class 377 - Southern / Third rail / Square windows

Refurbishment in progress

377/1 - 4 coaches, 101-139 have old lights

377/2 - 4 coaches, dual voltage
377/3 - 3 coaches, former Connex SE 375311-338

377/4 - 4 coaches

4 coaches sets may have 3+2 seating in middle carriages

Class 377 - Southeastern / Square windows

377/5 - 4 coaches, dual voltage, former FCC/Thameslink

Southern interior, 3+2 seating in middle carriages

Class 377 - Southern / Round windows

377/6 - 5 coaches, "ironing board" 2+2 or single seats, third rail only

377/7 - Same as above, with extra dual voltage compatibility intended for services to Watford Junction (or further)

Class 378 - London Overground / Metro

All variants are now extended to 5 coaches

Horizontal seating w/ pocket sliding doors, doorway standees, and 2 wheelchair areas

378/0 - built as 3 coaches, dual voltage, renumbered to 378/2 upon extension to 4 coaches

378/1 - built as 4 coaches, third rail only

378/2 - built as 4 coaches, dual voltage

Class 379 - Overhead wires / Round windows

Formerly with Greater Anglia for use on West Anglia Routes including to Stansted Airport
Now gradually rolling out onto the Great Northern route from London Kings Cross to Letchworth, Cambridge, Ely and Kings Lynn

379(/0) - 4 coaches, 2+2 (standard class) or 1+2 seating (first class)  / Not ironing boards

Class 387 - Dual voltage / Round windows

2+2 ironing boards w/ luggage racks, 4 coaches

387/1
101-129 - Great Northern / Southern (transferred from Thameslink)
142-171 - Great Western Railway
172-174 - Southern (kidnapped from GWR)

387/1a
130-141 - Heathrow Express (converted from / provided and maintained by GWR)
First Class area has 1+2 seats, tables removed in favour for drink holders, ETCS fitted for Heathrow tunnels

387/2
201-229 - Gatwick Express / Southern units

387/3
301-306 - Porterbrook stock-built / Initial C2C fleet, transferred to Great Northern then Southern
De facto completely same as GN 387/1s but with blue doors instead of green

Leasing / Transfer history

Some effort has been made to ensure this section is as accurate as possible
Please do message me in case any information below is not correct
Last updated 20/02/2025

Due to intense and unstable movements of certain units between Southern and Great Northern,
some of those movements will NOT be individually detailed

Class 377 (Currently transferred)

121, 122: Southeastern, Southern livery debranded

Class 377 (Former leases)

163, 164 - Southeastern, Southern livery debranded
201, 207, 208, 209, 210, 211, 212, 213, 215 - First Capital Connect / (Govia) Thameslink, SN debranded or w/ Govia TL logos
*FCC Urban Lights livery applied on 207, 211, 212 (https://units-library.weebly.com/class-377--2.html, https://ukrailwaypics.smugmug.com/UKRailwayPics/Electric-Multiple-Units/Class-377/)

Class 387 (Currently transferred)

101-129 - Thameslink > Great Northern (some > Southern), replaced at Thameslink by Anglo-German forces (Siemens Desiro City / Class 700)
301-306 - C2C > Great Northern (some > Southern), replaced at C2C (with delay) by Class 720/6 Aventras

Class 387 (Previous records)

172, 173, 174 - Great Northern, GWR livery debranded (in various ways Hornsey can offer)

201, 207, 209 - Great Northern, white logos
202, 203, 204, 205 - Great Western Railway, GX debranded
202 - Great Northern, purple logos (after GWR)

301, 302, 306 - Great Western Railway, Green GWR logos