Lara Parmiani provides expert coaching for those wanting to start a voiceover career: www.laraparmiani.com
London, as the European headquarters of big multinational corporations and TV channels, produces a lot of work in foreign languages. So if you're an actor and your native language isn't English, there's potentially quite a bit of work to grab.
Lots of big agencies have a foreign section, and none of them will ask you to be exclusive so you could potentially sign with fifteen different agents and be sure they'll never clash as they would be dealing with different clients.
HOWEVER... It's not all that rosy....
If fifteen years ago being a native speaker was all it took (the alternative being flying somebody over or spending a week looking for agencies abroad who might be able to organise an ISDN session), nowadays within minutes producers can search the internet for artists based in Portugal, India, or China, book a Source Connect session, and record them in real time here.
If they're on a tight budget they can even find somebody with their own home studio. Of course, it's a bit fussier (different time zones, currencies, language barriers etc), but it gives them the chance to work with the "real deal". Therefore as foreign VO artist in London you are now competing with the pros back home. And it's fierce. NO cheating allowed! You're expected to be as good as anyone you hear on TV or radio in your own country. True, lots of agents won't be able to tell the difference as they don't speak the language. But clients commissioning the job will always be able to tell. And if you don't fit the bill, they'll never call you again.
So be honest. Do you have the right accent, intonation, delivery? In most countries VO talents speak with the local equivalent of the British RP. Can you do it? Do you know which styles are popular back home? Which voices? If the answer is no, you need to work on it.
When you're ready, record a reel with 5-6 tracks in your language and just ONE track in English. Yes just one. And with your native accent! That's what agents want to hear, your accent will get you work, not your ability to sound almost English, you'll find there's plenty of English speakers in England...
Make sure you have not only commercials but also different narrations, as the bulk of work for foreign voices is corporate and technical stuff. Make sure you can sight-read anything in your language, from computer jargon to pharmaceutical terms because you'll often be in sessions where you'll be the only native speaker. And invest in a basic home studio. It'll allow you to work for people back in your country from your bedroom in London.
No more Ryanair flights at 6am... Have fun!