Our electoral system is skewed against small political parties – it's well known.
Perhaps the most obvious problem is the "first past the post" system of single constituency MPs elected to represent large areas by the largest number of votes but without a requirement for a majority. Thus, most of our representatives in Parliament got the largest number of votes in their constituencies, but do not have the support of the majority of the voters.
This translates to a Government that is hugely unrepresentative of the people. So-called "minor parties" in British politics can gather a significant proportion of national vote, but never be the largest party in any one constituency and never get any representatives in the House of Commons.
While there are many benefits to democracy from our system (stability, direct representation), the drawbacks lead to a feeling of distance and disenfranchisement. The incumbent major parties see no benefit to themselves in a change in the system and there is a consequent disillusionment and Sinicism among voters.