Mostly atoms and molecules will have London dispersion force. HCl being a polar molecule will have dipole-dipole interaction. Though HCl is having London dispersion force, the dipole-dipole interaction is more.

All molecules and atoms have London dispersion (i.e. van der Waals) forces. With HCl , a polar molecule, all we say is that the predominant intermolecular force is dipole dipole interaction.

dipole-dipole
Dipole-dipole forces are somewhat stronger, and hydrogen bonding is a particularly strong form of dipole-dipole interaction….Boiling Points and Bonding Types.

HCl molecules, for example, have a dipole moment because the hydrogen atom has a slight positive charge and the chlorine atom has a slight negative charge. Because of the force of attraction between oppositely charged particles, there is a small dipole-dipole force of attraction between adjacent HCl molecules.

Just imagine the towels to be real atoms, such as hydrogen and chlorine. These two atoms are bound to each other through a polar covalent bond—analogous to the thread. Each hydrogen chloride molecule in turn is bonded to the neighboring hydrogen chloride molecule through a dipole-dipole attraction—analogous to Velcro.

To form an inert gas electron configuration, each atom in HCl requires one more electron. The size of the atom, considering its electronegativity, is such that its electron density is too low for hydrogen bonds to form. This is why, while HF does, HCl does not demonstrate hydrogen bonding.

An ion dipole force exists between an ion and the partial charge on the end of a polar molecule. HCl is a polar molecule, for example, because the electronegativities of the H and Cl atoms differ. Positive ions are attracted to the negative end of a dipole, whereas negative ions are attracted to the positive end.

The London dispersion force is the weakest intermolecular force. The London dispersion force is a temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. This force is sometimes called an induced dipole-induced dipole attraction.

HCl molecules, for example, have a dipole moment because the hydrogen atom has a slight positive charge and the chlorine atom has a slight negative charge. Because of the force of attraction between oppositely charged particles, there is a small dipole-dipole force of attraction between adjacent HCl molecules.

The strength of London dispersion forces depends on the size of the molecule or atom . Larger atoms and molecules have more electrons. This leads to larger dipoles being established.

Another example of a dipole-dipole interaction can be seen in hydrogen chloride (HCl): the relatively positive end of a polar molecule will attract the relatively negative end of another HCl molecule. The interaction between the two dipoles is an attraction rather than full bond because no electrons are shared between the two molecules.

Answer: London dispersion / van der Waals forces are caused by distribution of electrons throughout the molecule / atom of the compound.