As you move on through London, you will enter the heart of the Reaper’s offense against the humans. This area will be flush with Brutes and Ravagers, as well as lesser enemies like Cannibals and Marauders. Head into the building through the opening on the left. Make another left once you are inside and take cover behind the vehicle. A group of Husks will rush you as you get into cover. Hit them with an area of effect attack, like Singularity or Grenade, to take out as many as possible. Mop up the rest with close range attacks or Shotguns. Right on cue, when you fell the Husks, a group of two Brutes will charge out. You can use one of two strategies here. First, you can order your squad-mates to focus their attacks on one Brute while you attack the other. This can be an especially effective tactic if you have the Incendiary Ammo ability activated, as your bullets will chew through the Brutes’ armor like it was nothing.
The alternative is to focus on the Brutes one at a time. With both you and your squad-mates focusing on the same Brute, it will stand little chance. This is especially effective if you don’t have Incendiary Ammo, since you will have to combine forces to deal more damage without that potent effect giving your shots an extra kick. Use your squad’s Biotics rapid fire to reduce the first Brute’s armor to nothing, and then repeat the process on the second. If you have a good Shotgun (again, the Spike Thrower is ideal when fighting Brutes) pepper them with gunfire in between volleys of Biotics. The only caveat to this strategy is that the Brutes are very mobile foes, and it can be easy to confuse one Brute for another. Use the health bars at the top of the screen to differentiate which one you are aiming at.
Vanguards, on the other hand, need not worry about strategy during this encounter. Simply Biotic Charge from one Brute to the other, use Nova to deal heavy damage to both, and then equip the Spike Thrower to fell both in a matter of seconds.
Head to the far side of the room. Climb up the ladder here and take cover on the second floor. You will be walking into this section of the building from the side, and all of the enemies in this room will be shooting out through the front. The squads below will radio you and desperately request support. Depending on how you play it, you can have a huge advantage in this encounter by sweeping through the upper floor from the side. You will have to play it carefully, though, as there will be a Ravager between the two Marauders on the turrets, and it can be difficult to get a great line of sight on this heavy enemy thanks to all of the debris strewn about the office.
While you have the element of surprise, toss a Grenade (or Singularity, if you don’t have any Grenades) targeting the Ravager right between the two Marauders. This will hit the Marauders with splash damage while dealing heavy damage to the Ravager as well. Immediately afterwards, destroy the two Cannibals by the door, who will now be turning to attack, with a Shotgun or charged melee attack, and take cover on the wooden desk where they stood a second ago. Use the cover in case the enemy forces become overwhelming, but pop out as soon as you can to finish off the two Marauders who were using the turrets.
After you’ve taken out these main threats, you will only have a few enemies to take care of on the other side of the room, mostly Cannibals and a few Marauders. Send your squad around one side of the arena and run around the other side yourself to catch the enemies in a pincer movement. Crush them between your two forces to kill them easily. Search the right side of the room to find a Med Kit, then search by the damaged door, underneath the gurney, to find another one. Examine the console on the wall to get a few credits, and then proceed through the open door to the back of the area.
When you go to open the door, a group of Husks will burst through and attack. Kill them quickly and head through the now-opened door. Run down the hall and drop down on the other side to reach the road again. Head down the street, but find cover soon, as yet another group of enemies will attack you here. Look to the left to find a small group of enemies rushing you on the other side of the crashed vehicle. Take them out while your squad focuses on the enemies up and to the right. Command your squad to stay put. They should be firing on the enemies to the right, near the building, still. Loop around the left side of the crashed vehicle, killing any enemies who remain over here along the way, and take cover to the side of the car. Aim around and fire upon the enemies in the building while your squad shoots at them from their initial position. Catch the enemies in the crossfire and watch them fall quickly. Kill the Ravager first, as it will pose the greatest threat.
Your plan will be interrupted mid-combat when another Brute charges out from behind the building. Immediately switch the focus of your squad to deal with this new threat. Have them all focus fire on the Brute, and use Warp, Warp Ammo, Incinerate, Incendiary Ammo, or another armor-killing power to whittle down the massive Brute’s health. Ideally, you will be able to kill the Brute before it reaches the wide open area of the street. If it reaches this spot, it will have free reign to charge about and attack you from multiple directions. It should die soon regardless, though. Return your focus to the remaining enemies in the building. Kill the ones in the front of the building and prepare to make an assault on the remaining Reapers inside.