No there is no shuttle - it takes about two hours on the dlr and tube. Not sure on a taxi, it would depend on traffic...

How much time do you have in between flights?

That's a horrible connection - you do realise these two airports are literally on the opposite side of the largest most congested city in western Europe? I can't imagine how long it would take to do that journey in a bus or taxi, especially at busy times of day. Public transport possible in just over an hour but lots of changes of tube/rail.

I have done the trip a couple of times but I prebooked a taxi, journey took couple hours but it would depend on the time of day.

Taxi to Paddington and Heathrow Express to Heathrow would cost at least 60 GBP, probably more. Taxi from London CIty to Heathrow will top 80 quid ($130).

Look into a car service, which will still probably cost 50 quid.

Or change your arrangements, which may only cost a little more and save you 1.5 to 2 hours of travel time between airports.

The first question is - how long do you have for the journey? If less than 4.5 or 5 hours (bearing in mind check in/security at LHR) you probably need to re-book something.

How about train to Waterloo-East and then train from Waterloo to Feltham, a stone's throw from Terminal 4 and served by air buses to all terminals. All by train and much cheaper I suspect that Heathrow Express, whose cost can be cut by taking the slightly slower Heathrow connect, a stopping train running over the same tracks.

There is no train from city airport period. It is serviced by the dlr only and that line goes into Bank. You will need to take the Dlr to Canning Town, change to the Jubilee line to Green Park, then the Piccadilly line to Heathrow. Allow two hours for the transfer...I live on this dlr line and do the commute every time I use Heathrow and it takes two hours, assuming all the transit works. Be prepared to carry your luggage up and down stairs at Green Park.

Or you could change at Westminster to the westbound District Line, take an Ealing or Richmond train and change to the Piccadilly at Hammersmith - much easier (escalators at Westminster and just a few steps across the platform at Hammersmith).

If you really have to get from one to the other and can't change your flight to one into Heathrow, that is.

I agree Patrick, but then they will have to leave more time as the District line takes a bit longer (I tried that route once...)

and bear in mind - that 2 hours is just for the journey. Not for airport formalities, luggage, whatever

There is no train from city airport period. It is serviced by the dlr only and that line goes into Bank.>

But the DLR does go to Greenwich (or a rail station near Greenwich) right which has rail links to Waterloo-East and is connected to Waterloo mainline station which has frequent trains to Feltham. Yes cumbersome but not more so than any other proposals here I think.

That would require a change at Poplar, a change at Greenwich, a change at Waterloo East that involves walking thought the extremely busy Waterloo Station then a walls from Feltham to terminal 4,, then a shuttle bus to the appropriate terminal...a huge hassle compared to the two changes required to take the dlr, jubilee line and then the piccaddily line...

But by far the best option, if available, is to change the inbound flight to come into Heathrow.

Ah, PatrickLondon gets it!

There is a natural relationship between time and money. You can substitute one for the other but there very few things in life that are cheap and fast. Well, perhaps JetBlue, but there are always exceptions!

Yikes!!!! Thank you all very much for your responses. I thought of changing the 1st flt., but it cost quite a bit for 2 people to change their flt. however, I may just call the airline & tell a supervisor (if that matters???) that BA should never book a flt into LCY connecting with one out of LHR. I guess it is worth a try to change.
Thanks again.

I meant to mention we have 4 hrs. to make the connection. Land at LCY at 7:05 a.m. Tues. connect at LHR on a 11:20 flt.

It sounds like this is one booking. If so, you are protected - meaning if you miss the connection they will put you on the next available flight out of LHR. But two possible problems - there may not be available seats right away, and if BA considers this a legal connection and you are late - they could determine that you 'dawdled' and missing it was your fault.

You will likely have both boarding passes - but you'll still have to clear immigration and customs at LCY (easy) and security at LHR. Plus it will be during the morning commute so transport will be crowded.

But if they won't change the flight times, and if you run, you have a reasonable chance.

(If it isn't on the same booking - forget all of the above a )