I am applying for a Tier 5 Youth Mobility visa, but have been refused a visa/overstayed in the Czech Republic/Schengen zone [duplicate]

The strategy of concealing an adverse immigration event by 'losing' one's passport and getting a fresh, unblemished passport is a poor one. There is a history associated with the passport that is not accounted for in its physical pages, but rather in computer systems linked to the passport number. And a new passport will contain a record linking it back to the previous one. People still try this strategy, however, and when they get caught the results are catastrophic.

If the UK catches somebody doing this, they will get logged (along with their biometrics) as violating Paragraph 320 of the Immigration Rules. That usually means the person can forget about coming here for a long time, if ever. Plus they will tell the US Department of Homeland Security about it (regardless of your nationality). They keep your biometrics on file for 12 years if you have a clean history, and indefinitely if you fall under Paragraph 320.

For your other question, if the refusal of a work permit in the EU has plays a role in the UK's decision process, the answer is yes, but refusal is not a foregone conclusion and a prior refusal is not a show-stopper. They will need to examine the circumstances of your refusal vis-a-vis changes in your circumstances that they consider remedial. If they conclude that your circumstances have changed, your refusal in the EU will be irrelevant.

Finally, if they find out you overstayed a visa in the EU, they will be upset and entitled to conclude that you do not honour the terms and conditions of visas. Alternatively if you conceal it, matters can become infinitely worse (Paragraph 320 again). Also, if the form asks you straight out for a list of countries you have visited, you should list them.

Overall, if the form asks a question, you should consider it relevant and important and provide as much candour as you can. Paragraph 320 is here https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/370958/20141106_immigration_rules_part_9_final.pdf

If you are worried that your T5 application may be imperilled, you can instruct a UK based specialist to help out. http://www.ilpa.org.uk/pages/find-immigration-advice.html

Never lie on applications.

The stamp in your passport is NOT the only record that you've had your previos attempt rejected, I assure you.

However, having a rejection does not necessarily mean you'll get rejected again. Overstaying visas certainly doesn't help, but I have a friend who overstayed his visa, was caught, and has since been back on a tourist visa - it just required more effort and details in the application.

Countries also share information. A relative had her returning residence visa expire for a country, and upon boarding a flight to there, the departure country could tell this on their system, and she had to spend a day frantically running around sorting out an emergency visa for this.

GIven your situation, and that you've been declined AND have a previous overstaying record, I'd highly recommend speaking to an immigration advice specialist - they'll often be able to help you with the right wording to appease the visa approvers.

Don't leave anything out, don't lie, and don't obscure any details. If you follow the process with the right advice, it prevents any further stuff going wrong. If you're caught lying/ommitting, you're definitely going to have a big black mark on your record after that.