There has been sleaze when Labour have been in power as well. MPs have legalised corruption for themselves, by allowing all sorts of perks and benefits and payments to be considered acceptable. It is also very hard to hold an MP to account.
It is hardly surprising that it is a job that attracts corrupt, even evil people.
When MPs are banned from having second jobs, they cannot make extra money by being consultants to industry or any other campaign group, they cannot employ family or friends as assistants, they are provided with accommodation in London and offices in their constituency that they moves to the next MP who gets elected, they are not given subsidies to buy or rent or run their own places, the restaurants and bars in Parliament are not subsidised and the expenses they can claim have to be directly related to their work, then we will see a fall in the level of corruption.