Utilize the input text as a context reference, choose the right relationship between G4S and London from the options. Options: product/material produced, manufacturer, distributed by, industry, position held, original broadcaster, owned by, founded by, distribution format, headquarters location, stock exchange, currency, parent organization, chief executive officer, director/manager, owner of, operator, member of, employer, chairperson, platform, subsidiary, legal form, publisher, developer, brand, business division, location of formation, creator.

Market Movers techMARK 3,181.87 +0.60% FTSE 100 6,623.51 +0.80% FTSE 250 17,591.53 +0.88% FTSE 100 - Risers Coca-Cola HBC AG (CDI) (CCH) 1,437.00p +8.62% TUI AG Reg Shs (DI (KSE: 003160.KS - news ) ) (TUI) 1,120.00p +7.18% London Stock Exchange Group (LSE) 2,596.00p +2.89% 3i Group (III) 531.50p +2.71% ARM Holdings (LSE: ARM.L - news ) (ARM) 939.50p +2.57% Inmarsat (LSE: ISAT.L - news ) (ISAT) 1,000.00p +2.56% ITV (ITV (LSE: ITV.L - news ) ) 260.90p +2.56% Hikma Pharmaceuticals (LSE: HIK.L - news ) (HIK) 2,345.00p +2.54% Admiral Group (LSE: ADM.L - news ) (ADM) 1,469.00p +2.51% Burberry Group (Other OTC: BBRYF - news ) (BRBY) 1,517.00p +2.36% FTSE 100 - Fallers G4S (Amsterdam: GF6.AS - news ) (GFS (Taiwan OTC: 6026.TWO - news ) ) 258.40p -4.26% Rio Tinto (LSE: RIO.L - news ) (RIO) 2,493.50p -2.39% Royal Mail (LSE: RMG.L - news ) (RMG) 481.70p -1.99% Randgold Resources Ltd. (RRS) 4,087.00p -1.90% BT Group (LSE: BT-A.L - news ) (BT.A) 454.85p -1.42% Ashtead Group (LSE: AHT.L - news ) (AHT) 965.00p -1.33% Pearson (Amsterdam: PR8.AS - news ) (PSON) 1,151.00p -1.29% Royal Dutch Shell (Xetra: R6C1.DE - news ) 'A' (RDSA) 1,865.50p -0.64% Royal Dutch Shell 'B' (RDSB) 1,878.50p -0.63% Diageo (Amsterdam: DO8.AS - news ) (DGE) 1,767.00p -0.45% FTSE 250 - Risers Playtech (PTEC) 914.50p +4.99% Allied Minds (Other OTC: ALLWF - news ) (ALM) 491.40p +4.73% Ashmore Group (Other OTC: AJMPF - news ) (ASHM) 263.90p +4.23% Cineworld Group (LSE: CINE.L - news ) (CINE) 569.50p +3.83% Rightmove (RMV) 3,758.00p +3.81% Michael Page International (Other OTC: MPGPY - news ) (MPI (Other OTC: MNIGF - news ) ) 545.00p +3.42% Thomas Cook Group (TCG) 116.00p +3.20% Just Eat (Other OTC: JSTLF - news ) (JE.)

Answer: headquarters_location