かなり忙しない

//www.britishairways.com/travel/airpflcnxlhr/public/en_gb

Connecting at London Heathrow

ヒースローで Fast Trackが使えると随分楽になるのですが。
しかし、極く一般的なことだけしか書かれていない。

空港サイトの、
International Flight Connecting to an International Flight
Connecting from Terminal 5 to ...Terminal 5

Welcome to Heathrow. On leaving the aircraft please follow the signs for Flight Connections.

If you wish to visit your airline’s ticket desk you will find it at this point.
これは成田ですでに搭乗券を持っているので不要。

Staff will check your ticket to ensure you are in the right place and that you have sufficient time to catch your onward flight. They will also check that you are not carrying too many bags and that your bags conform to airline size restrictions.
Your hand baggage must conform to EU and UK government regulations. At this point your hand baggage will be checked. Please note, liquids in containers over 100ml are not allowed through security. More information about security.

You will pass through security screening at this point. If you are a non-UK resident and have goods to declare to H M Customs, please use the telephone prior to Security to contact a member of staff.

Once you arrive in the departure lounge you will be ready for your next flight. Check the screens for information about your flight, as they will tell you when to go to your departure gate. Meanwhile, you can relax, shop, eat and use other facilities here. Please note there are no service facilities or shops at the departure gates.

往路が85分、復路が95分なので、前の便が遅れなければまず問題はないでしょう。
しかしです。ターミナルができても、離発着数の過多は解消されていない。
何時も工事中の空港で、継ぎ接ぎだらけです。

まず、定刻通りロンドン上空に来ても、着陸の順番待ちで先回。
駐機場に空きがあるか、検査場の混雑など、関門は山積みです。

入国カードは記入しても構いません。記念になるだけですが（使い道がないので
捨てることになるでしょうが）。

繰り返しになりますが、遅れがなければ、丁度良い接続時間です。
逆に遅れると大変ですが、英国航空がなんとかしてくれるので心配なく。