just wanted to give my experience in this regard:
I have let out my flat in UK since the day I came to CH in 1999
I have delcared the asset in CH with the income less deductions in UK and in CH with my CH income.
In UK I paid no tax as net UK income was less than yearly personal allowance
In CH I paid less tax than otherwise as the yearly accounting loss was offsettable against CH tax liability.
In March 2007 I got a letter from UK-HMRC that I no longer need to submit returns after the the one for Apr5th 2007-yippee!
In CH the value is assessed each five yrs so I benefited from only "delayed" additional wealth tax liability despite regular increases in valuation.
Now this CH declaration history is useful for financing my impending purchase in CH.
The admin impact was having to make two simple spreadsheets showing per month incomings and outgoings and my yearly mortgage interest payment, with the deductions from my UK return for wear & tear, repairs etc, about 1 hrs work for each country. The CH return allows you the choice of a 20% offset or real amounts. My UK property is managed and they send me monthly PDFs which I tot up in my spreadsheet.
Luckily I have a steady tenant and would just love to re-mortgage for lower interest rates somewhere like in liechtenstein
Hope this experience summary helps. If anyone wants my spreadsheet templates, let me know.